This study examined associations between Mexican-origin parents’ cultural values in relation to supportive and undermining coparenting behavior. Data were collected from 80 sets of parents, 160 parents total, with a preschool-age child ( M = 63.60 months old; 39 boys, 41 girls) who were of Mexican origin (22% of mothers and 28% of fathers born in Mexico). Mothers and fathers independently completed questionnaires assessing their cultural values of (a) familismo (i.e., loyalty to family), (b) machismo (i.e., adherence to masculine/feminine gender roles), (c) respeto (i.e., respect for self and others), and (d) simpatía (i.e., maintenance of interpersonal harmony). Mother–father–child triads were observed during a structured play session from which supportive and undermining coparenting behavior was coded. Mothers and fathers who held stronger familism beliefs were characterized by more supportive coparenting behavior. Mothers and fathers who held stronger simpatía beliefs were characterized by less undermining coparenting behavior. Fathers who held stronger respeto beliefs showed more supportive coparenting behavior, whereas mothers who held stronger machismo beliefs were characterized by more undermining coparenting behavior. Mother–father dyads with higher agreement on familism displayed more supportive coparenting behavior, and mothers and fathers who had higher agreement on simpatía beliefs engaged in less undermining coparenting. Results suggest that the cultural values held by both mothers and fathers of Mexican origin are significantly associated with the quality of their coparenting relationship.