Background: Social participation (SP) is known to have a favourable impact on health. However, studies on this issue have been conducted mainly in advanced countries, and results in China have been mixed. This study examined the impact of SP on health outcomes of middle-aged and elderly adults in China, adjusted for simultaneity and heterogeneity biases. Methods: In total, 57,417 observations of 28,935 individuals obtained from the population-based, three-wave panel survey, Chinese Health and Retirement Longitudinal Study (CHARLS), conducted in 2011, 2013, and 2015 were used. The associations between one-or two-wave-lagged SP and health outcomes (mental health, self-rated health [SRH], activities of daily living [ADL], and diagnosed diseases) were examined by linear regression models. Individual-level heterogeneity was addressed by the random-effects estimation method. Results: SP was found to have a positive impact on mental health and ADL. Specifically, one-wave-lagged SP improved mental health measure (range: 10-70) by 0.820 (standard error [SE]: 0.199, p < 0.001), the basic ADL measure (range: 6-24) by 0.147 (SE: 0.043, p < 0.001), and the instrumental ADL measure (range: 5-20) by 0.159 (SE: 0.035, p < 0.001). In contrast, SP did not significantly affect SRH or diagnosed diseases. The impact of SP differed by SP type; playing Mah-jong (Chinese traditional game), chess, or cards, or going to the community club had the most favourable effect. The impact of SP on health was also greater for women than men and greater for individuals aged 60-69 years than those aged 45-59 years and aged 70 and older. Conclusions: SP had a positive, albeit selective, impact on health outcomes among middle-aged and elderly adults in China. The results suggest that policy measures to encourage these individuals to engage in SP are needed to enhance their health.