Japan withdrew from the International Whaling Commission, or IWC, on Sunday. The country will resume commercial whaling the next day.
Japan joined the IWC in 1951, supporting its pursuit of sustainable whaling by protecting the number of whales.
After Japan suspended commercial whaling in 1988 in line with an IWC moratorium, it has been unable to find common ground with anti-whaling countries.
Japan announced its intention to withdraw last December, saying it was no longer possible to resume commercial whaling under IWC rules.
Several whaling ships are ready to leave the western port city of Shimonoseki, Yamaguchi Prefecture, on Monday to start whaling in the Pacific.
And in the northern city of Kushiro, Hokkaido Prefecture, five vessels plan to leave for whaling in nearby waters.
Japan says it will conduct commercial whaling only in its territorial waters and exclusive economic zones, hunting minke and other species that have large enough numbers, within quotas set by the IWC-adopted method.
Environmental activists are criticizing the resumption in light of resource conservation and animal protection.
The Japanese government plans to gain support from the international community by stressing that hunting will be done within the limit to preserve the whale population.