The protesters left Hong Kong Sunday headed for the Senkaku Islands, calling for an end to "Japanese militarism," Kyodo News reported.
Action Committee for Defending the Diaoyu Islands will be joined at sea by two other vessels, said Chan Miu-tak, the leader of the group.
The islands are known as the Senkaku to the Japanese, while the Chinese call them Diayou.
On Friday, South Korean President Lee Myung Bak visited another set of islands claimed by Japan and said the Diaoyu islands were Chinese territory.
Chan said he hoped the Chinese government would not stop the boats. Hong Kong has barred protest vessels from leaving its waters, and Beijing has been reluctant to allow civilian protests over the islands.