Young women experience a range of body-related threats (e.g., appearance comparisons, weight-based teasing) in their everyday life, which may negatively impact physical activity motives and behaviour. Self-compassion – a self-directed response to threats with acceptance, kindness, and understanding – may buffer the negative effects of body-related threats and contribute to more adaptive physical activity motives. To date, research on how body-related threats, self-compassion, and physical activity motives naturally fluctuate in daily life has been scarce. As such, the present study examined state-level relationships between experienced body-related threats, self-compassion, and physical activity motives. Young adult women (n = 127; Mage = 20.63, SD = 2.11) completed a 7-day mobile ecological momentary assessment protocol with 7-daily surveys. During instances when women experienced a body-related threat, they reported higher engagement in appearance-motivated physical activity (? = 1.32, 95% CI[0.58, 1.96]), ability-motivated physical activity (? = 0.89, 95% CI[0.23, 1.66]), and health-motivated physical activity (? = 0.78, 95% CI[0.18, 1.45]). Among women with higher average levels of self-compassion, the frequency of body-related distressing situations was associated with higher motives for engaging in health-related physical activity (? = 0.28, 95% CI[0.07, 0.46]). Frequency of experiencing body-related threats across the week was not significantly associated with physical activity motives. These results emphasize the importance of using momentary assessments to study how body-related threats impact fluctuations in physical activity motives in daily life. Further, the results provide preliminary support for the utility of cultivating self-compassion as a strategy to promote adaptive physical activity motives in response to body-related threats.