Purpose This study aimed to examine the relationship between participation in social activity and both, composite and individual measures of physical fitness in community-dwelling older adults.Methods This study was conducted using baseline data from the Sasaguri Genkimon Study (SGS), a longitudinal cohort study conducted in 2011. Participants were 1,365 community-dwelling men and women aged 65 years or above, who did not require certified nursing care and who resided in Sasaguri, a town located east of the Fukuoka metropolitan area. Participation in social activity was assessed by asking participants whether they engaged in any of eight social activities. Physical fitness tests assessed participants' handgrip strength and knee extension strength as measures of muscle strength, and their one-leg standing time, 5-m maximum gait speed, and 5-repetition sit-to-stand rate as measures of their physical performance. Multiple linear regression and logistic regression analyses were conducted to assess the relationship between participation in social activity and each measure of physical fitness, adjusting for sex; age; body mass index; socioeconomic status; solitary living; exercise, habitual drinking and smoking; accelerometer-measured, moderate-to-vigorous physical activity; cognitive function; instrumental activities of daily living; distress; social network; and comorbidities.Results A total of 83.6% of the participants were engaged in at least one social activity. After adjusting for potential confounders, engagement in social activity was positively associated with a higher composite physical fitness score, faster gait speed and 5-repetition sit-to-stand rate, and longer one-leg standing time (P=0.008, P=0.030, P=0.034, and P=0.009, respectively).Conclusion Participation in social activity was significantly associated with physical fitness, specifically those related to locomotive function. These associations were independent of various confounders including socioeconomic status, and comorbidities.