Changes to memory performance in the course of aging may be influenced by behavioral factors. The use of social media among elderly people is increasing, but studying its effect on cognitive functions such as memory remains at an early stage of development. Meanwhile, the linking mechanisms underlying the association between social media use and memory performance, if any exist, have not been revealed. This study attempted to examine the association between the use of WeChat, the most popular social media platform in China, and memory performance among older people, and to test the possible mediating role of depression underlying this association. Data were drawn from the five-wave survey of the China Family Panel Study (CFPS), and 4929 respondents aged 60 or older (mean age = 68.19, SD = 5.84, 48.2% females) were included. Based on the descriptive statistics, the chi-squared test, Student’s t-test, correlation analysis, and mediation analysis were conducted. The results indicated that the usage rate of WeChat among the sample was 20.1%. After controlling for demographic variables, the use of WeChat was related to higher levels of memory performance and lower levels of depression. Moreover, depression partially mediated the relationship between WeChat use and memory performance. To maintain memory performance and promote cognitive health in the course of aging, using social media and alleviating depression merit special attention.