Parent-child reminiscing talk about positive and negative events provides children with unique opportunities to develop emotion competence. Very little work has involved families from low-income households and ethnically diverse backgrounds. We examined: 1) event valence (positive vs. negative) and ethnic differences in mother-child reminiscing talk; 2) relations between maternal reminiscing talk and child emotion references; and 3) relations between maternal reminiscing talk and child emotion understanding. Participants were 204 African American, Dominican, Mexican and Chinese mothers and their first-grade children (M age = 79.50 months) from low-income households. Mother-child dyads were videorecorded talking about past positive and negative shared events. Conversations were coded for the emotion content and style of mother reminiscing talk and child emotion references. Child emotion understanding was assessed using an emotion-labeling and emotion perspective-taking task. Mothers differed in their use of emotion content and reminiscing style by event valence and ethnicity. Mothers who used more emotion content during positive and negative events had children who produced more emotion references. Maternal reminiscing style (i.e., use of evaluations and repetitions) related to child emotion references. Maternal emotion content and reminiscing style did not relate to child emotion understanding. Findings highlight the role of mother-child reminiscing talk in the development of children's emotion competence.