Childhood obesity is a risk factor for adult obesity and related diseases. Parent-based interventions, typically addressing maternal weight-related parenting practices (e.g., modeling, restricting, monitoring, limiting, and encouraging children’s diet, physical activity [PA], and sedentary behaviors [SB]), have been largely unsuccessful in preventing increases in children’s adiposity. Failure to assess how fathers’ weight-related parenting practices contribute to children’s obesogenic behaviors leaves a critical gap in the understanding of the etiology of childhood obesity. Additionally, research has focused on between-person methods, limiting inferences about within-day behavior changes in the same subject. To address these research gaps, the proposed study will use ecological momentary assessment (EMA) methods with real-time mobile surveys to examine the within-day effects of fathers’ parenting practices on children’s subsequent eating, PA, and SB. We will recruit 50 fathers whose spouses and 11 to 15-year-old children are current participants in the Mothers’ and Their Children’s Health (MATCH) study. Fathers will complete one 7-day assessment including EMA sampling. The primary aims are (1) to investigate acceptability, compliance, and user satisfaction of fathers completing a 7-day EMA protocol; and test hypotheses that: (1) fathers’ detrimental weight-related parenting practices (e.g., lack of encouraging healthy behaviors; lack of limiting unhealthy behaviors) will be directly related to children’s subsequent unhealthy eating, low PA, and high SB within the next few hours; and (2) fathers’ weight-related parenting practices will more strongly relate to girls’ (versus boys’) obesogenic behaviors (i.e., low PA, high SB, eating unhealthy foods). The proposed study is translational because it applies fundamental knowledge from two well-established areas of basic science research: (1) family-systems theory and (2) EMA methods development to address a critical gap in pediatric obesity research. The results from this study will inform development of a future parent-based child obesity prevention intervention using just-in-time smartphone-based intervention methodology to address parenting practices.