The current longitudinal study investigated the within-and between-person variance in work-to-family conflict and family-to-work conflict among working mothers over time. It also examined the effects of a nonstandard work schedule and relationship quality on work-to-family conflict and family-to-work conflict using bioecological theory. Results of multilevel modeling analyses showed that there was significant within-and between-person variance in work-to-family conflict and family-to-work conflict. The linear and quadratic terms were significantly related to family-to-work conflict, whereas the quadratic term was significantly associated with work-to-family conflict. There was also a positive relationship between a nonstandard work schedule and work-to-family conflict, whereas relationship quality was negatively associated with family-to-work conflict. Future studies should consider diversity among working mothers to adequately predict work–family conflict. The current study provides important implications for employers to consider, concerning within-and between-person differences among working mothers, which could in turn allow for accommodations and help to decrease work–family conflict.