Across all cultures, parents have intuitive ideas (“ethnotheories”) of what undesirable child characteristics are as well as how to explain them. Yet there have been relatively few cross-cultural comparisons of parents’ ethnotheories about the nature and causes of child misbehavior. 108 mothers of 5-year-old children from the United States (N = 52; Mage = 5.26, SD = 0.07) and mainland China (N = 56; Mage = 5.31, SD = 0.20) were recruited to participate in a semi-structured interview that allowed parents to generate open-ended responses in relation to the nature and causes of children’s misbehavior. Parents were asked to describe the behaviors they would least like to see in their children, before providing causal attributions to a series of hypothetical vignettes depicting a range of externalizing-type child behaviors. Parents’ responses were coded based on common themes. Across both cultures, mothers endorsed social insensitivity as the most undesirable child characteristic. With regard to cross-cultural differences, mothers from the US highlighted aggressive and disruptive behaviors as the most salient child misbehaviors, whereas parents from mainland China emphasized cognitive and motivational difficulties. Regarding causes of child misbehaviors, American mothers were more likely than Chinese mothers to report momentary internal states as the primary causes of child misbehavior, followed by immature development. Conversely, Chinese parents attributed child misbehavior primarily to social influences, followed by temperament. Our results provide a significant contribution to our understanding on how parents across cultures define and explain misbehaviors in young children.