This study used an ecological perspective to examine how daily variation in the time fathers spend in child-care activities was related to emotionally supportive or conflictual father-child interactions and whether fathers' negative mood moderated these associations. Data for the present analyses were from 2 daily diary studies. Both studies asked fathers to report about their daily experiences with their children, including how much time they spent with them and whether or not they had any supportive interactions or conflictual interactions. The first study used daily self-report questionnaires from a sample of fathers in rural upstate New York, and the second study used daily telephone interviews from a national sample of fathers. Results from a series of hierarchical linear models showed that fathers were more likely to have supportive and conflictual interactions on days when they spent more time engaged in child-care activities. The association between time with children and conflictual interactions was greater on days when fathers were in a negative mood. Negative mood did not moderate the association between time with children and emotionally supportive interactions. The findings from this study suggest that when fathers spend more time with their children they are more likely to engage in supportive interactions, regardless of negative mood.