The two-day meeting in Yokohama included experts, activists and lawmakers from 30 countries and 200 civic groups from across Japan.
Holding the meeting in the country of the Fukushima nuclear plant disaster was "significant," Tatsuya Yoshioka, conference chairman and director of Peace Boat, said.
After the plant was struck by the March 11 earthquake and tsunami, a series of blasts and fires triggered the massive release of radioactive material into the environment.
The plant operated by Tokyo Electric Power Co suffered meltdowns at three of its six reactors. More than 80,000 residents have been forced to leave the area.
"We have a strong feeling that we need to create a network beyond border to oppose nuclear power generation," Yoshioka said.