The relations among evaluation of supportive functions (ESF) of communitybased self-help groups (SHGs) for cancer survivors, benefit finding (BF), and mental health were investigated. Members of SHGs for cancer survivors (n=314) completed a questionnaire inquiring their background. They also responded to several scales, including the ESF Scale, BF Scale-Revised, and the 28 item Japanese version of General Health Questionnaire (GHQ28). Results indicated that the ESF of SHGs had a direct buffering effect on BF domains. Moreover, ESF of SHGs and BF were significantly mediated by age, time since diagnosis, participation status, and the role in SHGs. Results also indicated a significant relationship between most BF domains and "social activity obstacles" subscale of the GHQ28. These findings suggested that participation in self-help groups was helpful for increasing BF and BF played a role in recovering the mental health of cancer survivors.