Although dog meat restaurants are a dwindling business in South Korea, many citizens still eat the animals on what they believe is a special day.
Dozens of people opposing dog meat consumption, including American actress Kim Basinger, have rallied in Seoul to mark a "dog meat day" in South Korea.
About 20 others stood on the opposite side calling for the legalisation of dog meat.
There are no reports of violence.
Under a traditional belief, Friday is the first of the three hottest days in South Korea.
Many South Koreans believe eating dog meat or chicken soups on those three days gives them the strength to beat the heat.
Ms Basinger said: "We have to end this cruelty on this planet."
Dog meat is neither legal nor explicitly banned in South Korea.
Dog meat restaurants are a dwindling business in South Korea in recent years.