Chinese aging parents rely heavily on their adult children, while the causal effects of fertility decline on the intergenerational support are still unclear. This study uses China Health and Retirement Longitudinal Study (CHARLS) in 2015 to analyse how does the child number influence the living arrangements, instrumental support, emotional support, and financial support among Chinese families. I utilize the cohort-province-specific policy treatment as the instrumental variable (IV) to identify the fertility decline induced by the One-Child Policy. The results reveal that urban elderly parents can live closer to adult children and receive more instrumental and emotional support when they have fewer children. However, in rural families, the reduction of child numbers does not offer any benefits to aging parents; instead, it significantly reduces the amount of monetary support. My findings indicate the impacts of fertility decline are complicated, depending on the kind of support and where parents live.