Background
Grandparents play an essential role in childrearing and fill the parenting gap for dual-earner Chinese families. Many Chinese grandparents engage heavily in childcare, which may increase the risk of child abuse.

Objective
This study aimed to examine grandparental use of psychological and physical aggression toward children and explore its associated risk factors.

Participants and setting
This was a cross-sectional study which involved purposive sampling of 278 grandparents (204 females and 74 males) taking care of at least one grandchild below 18 years old in Shenzhen, China.

Methods
Information on childcare was collected, including grandparents' use of psychological and physical aggression and their involvement in childcare in terms of intensity and activity.

Results
An alarming percentage (57.1 %) of grandparents had used psychological aggression, while 26.5 % had used corporal punishment, in the past year. The average use of psychological aggression and corporal punishment was 16.10 times and 10.08 times per year, respectively. Grandparents taking care of two or more grandchildren were more likely to use psychological aggression and corporal punishment compared to those taking care of only one grandchild. Higher mental and physical health summary scores were associated with lower likelihood of psychological and physical aggression of grandparents.

Conclusions
This study advances our understanding of negative grandparenting behavior in childcare. As grandparents play a significant role in childcare, we need to improve their grandparenting skills, provide more formal childcare services to ease their childcare burden, and support their physical and mental well-being to reduce the risk of child abuse.