Purpose: Marital dissatisfaction and conflict often increase for couples after the birth of a child and are evident in fewer positive family interactions and more negative family interactions. Because exercise is known to increase positive emotions and decrease negative emotions, the current study examined the extent to which higher levels of mothers' exercise during the postpartum period were related to more positive and fewer negative emotion-expressive behaviors with their infants' fathers. Method: Mothers' (N = 46; M = 8 months postpartum) positive and negative expressive behaviors were coded during couples' discussions of current conflict and positive family experiences. Mothers self-reported their leisure-time exercise behavior. Results: First-time mothers and mothers with higher levels of leisure-time exercise behavior displayed higher levels of positive expressive behaviors during couples' discussions. Conclusions: Exercise may be associated with increased positive emotion and, in turn, can have great potential to improve family relationships during the postpartum period when marital stress normatively increases, particularly for mothers with more than 1 child. Future longitudinal studies are needed to understand exercise patterns across the postpartum period to identify the most effective timing and optimal level of exercise that lead to more positive expressive behaviors.