Literature suggests that social capital, which often promotes human welfare, requires sensitive handling to build and maintain. The current study investigated the role of extension officers (fukyu-shidoin) in Japanese agricultural and fishing communities, who help farmers/fishers in both technical and social matters. Past research found that in Japanese agricultural communities, extension officers’ activities, social skills, and relationships with their colleagues had effects on social capital and problem solving in communities. We conducted a nation-wide survey of fishery extension officers and found that the findings in agricultural communities were largely replicated in fishing communities with only one difference: Officers’ acitivities to provide a future vision had a positive effect for problem solving in agricultural communities. For fisheries, however, such activities were more effective when the officer had worked for the community for a longer period of time. This could be explained by the higher level of uncertainty in fishing than farming.