Research Findings: This study examined whether physical coercion and psychological control by mothers and fathers can influence preschoolers' use of physical and relational aggression, and whether the relations are moderated by children's effortful control in a Hong Kong Chinese sample. Data were collected from a sample of 168 children (88 girls; M = 60.97 months, SD = 5.51 months) and their parents twice, six months apart. At Time 1, mothers and fathers reported on their spouse's, as well as their own use of physical coercion and psychological control, and a puzzle box task was administered to assess child effortful control. At Time 2, mothers, fathers, and teachers completed questionnaires to assess child physical and relational aggression. Results show that mothers' physical coercion was associated with child physical and relational aggression. In contrast, fathers' physical coercion was significantly related to child physical aggression but its relation with child relational aggression was not statistically significant, and both these two associations were moderated by effortful control. Practice or Policy: These results suggest that general intervention efforts are needed to prevent aggression among children of physically coercive parents, and particularly among children with low effortful control and physically coercive fathers.