As a life event, fertility behavior has accumulative impacts on individuals' later-life health. This paper examines the effect of the number of births on Chinese older adults' depression by applying OLS and Probit models on data from the 2013 China Health and Retirement Longitudinal Study. Older adults with more children have more depressive symptoms. This negative association is more pronounced among those having three or more children. The mediation analysis suggests that the number of children affects the mental health of the older adults because it influences individuals' physical health and support from children. Analyses on the subgroups suggest that the influence of fertility on depressive symptoms is significant among rural older adults, adults aged 60-70 and older women. Other reproductive behaviors such as an older age at first birth and a longer reproductive period also adversely affect the mental health of older adults.