Parents and children with high negative emotionality may be more likely to provide and receive non-supportive contingencies, respectively. However, no study has examined child and parent negative emotionality in the same study and explored whether the link between child and parent negative emotionality may exist in part because of parental emotion socialization. The present study was designed to explore the link between the negative emotionality of mothers and their adolescent children and the potential mechanisms for this similarity. Maternal emotion socialization was explored as a mediator between maternal and adolescent negative emotionality, and between maternal negative emotionality and adolescent internalizing symptoms. Participants were mothers (M age = 30.47) with their children at two time points: preschool (Time 1; M age = 4.55 years old) and adolescence (Time 2; M = 13.73), with 81 boys and 94 girls. Negative emotionality was measured using a questionnaire, with mothers reporting for herself and her child. Maternal emotion socialization was measured by mothers’ self-report of their contingencies to their adolescent child’s negative emotions: 1) Punish; 2) magnify; 3) ignore; 4) override; and 5) support. The results revealed that the maternal punishing of the adolescent’s negative emotions was a mediator between concurrent mother negative emotionality and adolescent negative emotionality, such that higher mother negative emotionality was associated with more punishing, and more punishing was associated with higher adolescent negative emotionality, controlling for previous levels of maternal and child negative emotionality. Furthermore, being supportive of a child’s negative emotions was negatively associated with concurrent levels of adolescent internalizing symptoms, while magnifying a child’s emotions held a marginal positive association, controlling for previous levels of internalizing symptoms. The results highlight the importance of considering maternal emotion socialization strategies, even into adolescence, for a more comprehensive understanding of children’s emotional well-being. The findings have implications for developing and implementing emotion-based parenting interventions.