Objectives: In this paper, we assessed interdependent associations between food-related psychosocial traits and diet quality (ie, healthy and ultra-processed food consumption) among parent-adolescent dyads. Methods: This secondary analysis used data from the Family, Life, Activity, Sun and Health (FLASHE) study, which measured diet and other health behaviors in American parent-adolescent dyads (N = 1646). Actor-Partner Interdependence Models were used to apply a dyadic extension of the Theory of Planned Behavior and Social Determination Theory constructs (motivation, attitudes and self-efficacy) in relation to healthy and ultra-processed food (UPF) consumption. Results: Parent (b = 0.46, p < .01) and adolescent motivation (b = 0.42, p < .01) had positive actor effects on healthy food consumption. Parental attitudes had a negative actor effect (b = -0.20, p < .01) and adolescent attitudes had a positive actor effect (b = 0.34, p < .01) on healthy food consumption. Parent (b = -0.18, p < .01) and adolescent motivation (b = -0.14, p < .01) had negative actor effects on UPF consumption. No significant partner effects were found. Conclusions: Food-related psychosocial traits are associated with parent and adolescent diet quality. Interventions and guidelines that aim to strengthen an individual's ability to make healthful dietary choices, particularly those focused on reducing UPF consumption, are warranted, and may benefit from drawing on behavioral theories, especially those focused on motivational traits.