Self-conscious emotional experiences and evaluations of one's body are important predictors of physical activity behaviours Previous cross-sectional research has only demonstrated that body-related guilt is associated with moderate-to-vigorous physical activity (MVPA). The purpose of this study was to examine within-person associations between objectively-assessed physical activity and body-related shame and guilt, and the potential moderating effects of self-objectification beliefs. An analytic sample of 89 young adults (82.0% female; Mage = 19.53, SD = 2.22) completed a 7-day ecological momentary assessment (EMA) with 49 total prompts, assessing body-related guilt and shame at each prompt, while continuously wearing activPAL accelerometers. Data were analyzed using a mixed effect locations scale model using the program MixWILD. Lagged association between MVPA at EMA prompt t on participants body-related guilt and shame at EMA prompt t+1 was estimated. Additionally, predictors of within-person variability in self-conscious emotions were examined. Results showed that when participants were more active than usual at a prompt, they reported feeling less shame and guilt at the following prompt. Self-objectification did not moderate the within-person association between MVPA and shame or guilt. Less variability in participants' self-conscious emotion were observed when they engaged in more MVPA than average, indicating that when people were more active, they were better able to regulate their emotions. Findings support and extend existing cross-sectional evidence, demonstrating the relationship between body-related guilt and shame with MVPA in daily life. This research may suggest that engaging in regular MVPA may help regulate body-related self-conscious emotions of guilt and shame.