The fishermen and boats were seized March 4 and held at the Xisha Islands in the South China Sea, over which the countries had fought a decisive battle in January 1974, with China emerging victorious.
The area has remained a sore spot with Vietnamese fishers.
A statement from the South China Sea Fishery Bureau, under the Ministry of Agriculture, said after the detainees were released Friday they signed a written document stating they would not infringe on China's maritime and fishing rights in its territorial waters, the official Chinese news agency, Xinhua reported.
China alleged when a patrol boat seized the fishing vessels they contained 55 pounds of explosives along with tools used for dynamite fishing, Xinhua said.
Millions of Getty images now available for free via embed tool
Ray Liotta sues skin care company over use of likeness