Objectives: Our objective in this study was to establish the relationships among active and inactive physical activity, HRQoL, and weight stigma in children. Additionally, we investigated weight stigma as a mediator of the relationship between physical activity and HRQoL.Methods: This cross-sectional study was conducted in Hong Kong (June 2017-July 2018). Participants were 437 children in elementary school (2 primary schools and 2 non-governmental organizations) and their parents (dyads). Participants completed questionnaires containing items assessing demographic characteristics, physical activity level, and several HRQoL measures.Results: We found a statistically significant difference between a higher physically activity group (exercise > 2 hours/week) in all measures of HRQoL. Weight stigma had a significant mediating effect on the relationship between physical activity and child-rated HRQoL (Coefficient = -0.37; SE=0.05; t = 8.21; p < .001), parent-rated HRQoL (Coefficient = -0.16; SE = 0.04; t = 4.21; p < .001), and child-rated weight-related QoL (Coefficient = -0.56; SE = 0.04; t = 14.92; p < .001). Conclusions: Physical activity was associated with better HRQoL and lower weight stigma. Weight stigma appears to affect how physical activity is related to better HRQoL, but the association is somewhat weak.