The purpose of this study is to examine the evolution of social activities, activities of daily living (ADLs), and subjective health over time among the elderly aged 65 and older, and to test the longitudinal causal relationship between these three variables, as well as to identify differences by gender. To do so, we utilized data from four waves of the Korean Longitudinal Study of Ageing (KLoSA) from the fifth year (2015) to the eighth year (2018). Key findings include First, over time, social activity and subjective health decreased and assistance from others (ADLs) increased among the elderly. Second, we analyzed the longitudinal causal relationship between social activity, ADLs, and subjective health, and found that the higher the initial level of social activity, the lower the increase in ADLs and the higher the subjective health. Also, the greater the increase in social activity, the lower the increase in ADLs but the higher the increase in subjective health. Second, the greater the initial ADLs, the worse the initial subjective health, and the greater the increase in ADLs, the less the increase in subjective health. Third, the social activities of the elderly had a direct effect on subjective health, but indirectly through the mediation of ADLs. Fourth, multigroup analyses revealed group differences in the longitudinal causality of the three variables. Finally, based on these findings, suggestions were made to encourage social activities and improve health among the elderly.