This study examined the mediating role of children’s executive function (EF) in the relation between parental rejection and children’s externalizing behavior problems and whether this mediation varies depending on their callous-unemotional (CU) trait levels. Two hundred and eighty-four Chinese school-aged children and their fathers and mothers participated. Both fathers and mothers reported on parental rejection, children’s externalizing behavior problems, EF, and CU traits. The results showed that EF mediated the association between parental rejection and externalizing behavior problems. Moreover, the negative link between EF and externalizing behavior problems was moderated by CU traits; in particular, the combination of higher-level CU traits and lower-level EF predicted more externalizing behavior problems. Our findings point to the importance of considering family context and multiple personal factors simultaneously to decrease children’s behavior problems.