Demonstrators gathered outside the Japanese Embassy in Seoul on Friday, demanding Japan expresses regret for what happened in the past as “a nation of war criminals."
In another protest, protesters threw eggs at a post of Japanese products at a park in Seoul and called for a boycott of Japanese products.
An alliance of small business organizations said it has launched a boycott of Japanese imports.
The rallies come amid fresh tensions between the two countries over a series of long-disputed islets, known as Dokdo in Korean and Takeshima in Japanese, which are located in waters between South Korea and Japan.
The rallies were timed to coincide with the 94th anniversary of the start of Korea's struggle for independence in 1919.
Korea was ruled by Japan from 1910 until the end of the World War II in 1945.