Doyo no Ushi no Hi: Why Japan Eats Eel in the Heat of Summer

Learn what the midsummer Day of the Ox is, how its date is found, the popular story behind eating unagi, and how grilled eel is prepared.

Published October 20, 2026 at 11:03 AM JST | By Tokyo Paul

Quick answer: Doyo no ushi no hi, the midsummer Day of the Ox, is a traditional day in the hottest part of summer when many people in Japan eat grilled eel (unagi kabayaki). It falls on an ox day within the summer doyo period, the stretch of roughly 18 days before the start of autumn, so the date changes yearly and some years have two such days.

What the day is

The name has three parts. Doyo is a period of about 18 days before the start of each of the four seasons in the traditional calendar. Ushi means ox, the second sign of the Chinese zodiac. Hi means day. Doyo no ushi no hi is therefore an ox day that falls inside a doyo period, and the one that matters most is the summer doyo, which sits at the end of the rainy season and in the middle of the hottest weather.

In everyday speech the phrase almost always means the summer day and the custom that goes with it: eating eel. Shops, supermarkets and eel restaurants prepare for it in the days before, and many families treat it as a seasonal marker in the same way they treat other annual foods, such as the soba of New Year's Eve.

How the date is calculated

The old calendar assigned the twelve zodiac animals to a repeating cycle of days, so an ox day returns every twelve days. The summer doyo lasts around eighteen days, which means it contains at least one ox day and sometimes two. When there are two, they are twelve days apart, and the second is sometimes called the "second ox day".

Because the doyo periods follow the traditional calendar and the ox-day cycle runs separately from the months, the date shifts from year to year. A news data article, for example, lists two ox days in 2022, on 23 July and 4 August. To find the date for any year, look at a Japanese calendar or an almanac, and check the date on a current calendar before you plan a meal, since some years have one ox day and others have two.

The story behind the custom

The best-known tale credits Hiraga Gennai, a scholar of the Edo period who was also a writer and inventor. According to the story, an eel shop was struggling in summer, when eel was not considered a seasonal dish. Gennai advised the owner to put up a sign saying that the day was the day of the ox. Customers came, other shops copied the idea, and the habit spread.

This is a popular tradition and not a documented fact, so it is best told as "it is said that". A belief also linked to the day is that foods whose names begin with "u", such as unagi, udon and umeboshi (pickled plums), help people stay strong in the heat. The link between eel and summer stamina is much older: a poem in the Manyoshu, the eighth-century poetry anthology, is often cited as mentioning eel as something to eat to avoid summer weight loss.

Kabayaki, the usual way to eat it

Kabayaki is the classic eel dish. The eel is filleted, skewered, brushed with a sweet sauce made from soy sauce, sugar and mirin, and grilled over charcoal. The savory, caramelized glaze is the main flavor. A plain version grilled with only salt is called shirayaki, and some cooks use it as the base for sauce at home.

Regions prepare kabayaki differently. In the Kanto region, including Tokyo, the eel is opened from the back, steamed and then grilled, which gives a soft texture. In Kansai the eel is opened from the belly and grilled without steaming, which gives a firmer bite. Eel is commonly served on rice, as unadon in a bowl or unaju in a lacquered box, with a clear soup and pickles on the side.

According to the Ministry of Agriculture, Forestry and Fisheries, eel and rice were originally served separately, and the bowl form became popular partly because it kept the eel warm for delivery. The same page notes that grilling with soy sauce rather than salt became the mainstream seasoning, and that a sauce of soy sauce, sugar and mirin helped make the dish a hit in Edo.

Beyond kabayaki

Other eel dishes include uzaku, a vinegared salad of grilled eel and cucumber, and umaki, a rolled omelet wrapped around eel. Many supermarkets and convenience stores sell packaged kabayaki on the day. Home cooks often buy ready-made grilled eel, warm it gently and place it on rice, adding a little extra sauce if they like. Eel is often said to be fattiest in the cooler months, so the summer custom owes more to the story and to the seasonal habit than to the calendar of the fish.

Not everyone eats eel, and there are many other ways to join the tradition. Noodles such as udon and pickled plums are both u-foods. Choosing a u-food that suits your taste and budget keeps the spirit of the custom without the cost, and it is a friendly option for visitors who do not eat fish.

Eel and conservation

The Japanese eel is classified as endangered on the IUCN Red List, and its population is reported to be decreasing. Most eel eaten in Japan is farmed, but the farms depend heavily on wild-caught young eels, so supply is limited and prices are high. Governments in the region have discussed and agreed on measures to manage the number of young eels used for farming, and the details change over time.

Researchers in Japan have also worked on raising eels from eggs in captivity, a difficult process, but farming still relies largely on wild-caught young eels. For eaters, the practical points are simple: enjoy eel as an occasional treat, ask restaurants about their sourcing if you wish, and remember that other seasonal foods are welcome on the day too. Details of conservation rules change, so see official fisheries and environment pages for the latest information.

Practical tips for travelers

Eel restaurants can be busy around the day, and some take reservations, so planning ahead is sensible. Prices vary with the quality and size of the eel and the type of restaurant, and prices can be higher around the day itself. Many supermarkets and department stores sell packaged kabayaki in the days leading up to it.

The period is also very hot, so allow time to cool down and drink water. Check the opening hours and any special arrangements of a restaurant before going, as hours and menus can change. This guide shares general cultural information and published research, not professional advice; for health questions, talk with a doctor.

Frequently Asked Questions

When is doyo no ushi no hi?

It is an ox day within the summer doyo, the roughly 18 days before the start of autumn, usually in late July or early August. The date varies by year and some years have two ox days. Check a Japanese calendar for the exact date.

Why do people eat eel on that day?

A popular tradition says that Hiraga Gennai suggested an eel shop advertise the day of the ox in summer. Eel had also long been regarded as a strengthening food, and foods beginning with "u" are said to help in the heat. It is a custom rather than a rule.

What is the difference between Kanto and Kansai style eel?

In Kanto, including Tokyo, eel is opened from the back, steamed and then grilled, giving a soft texture. In Kansai it is opened from the belly and grilled directly, giving a firmer, crisper result. Both are basted with a sweet soy glaze.

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