Body positive movement has emerged to challenge the prevalent media depictions of thin-ideal bodies. Yet, there is not enough empirical evidence to evaluate the effffectiveness of body positive content on social media. Based on social comparison theory, this study examines the psychological and affective outcomes of body positive images on Instagram, along with the moderating role of social comparison. A 3 (body image type: thin ideal vs. neutral vs. body positive images) × 2 (state social comparison: high vs. low) online experiment was conducted. Results revealed that body positive images led to greater positive mood. Higher social comparison was related to lower body perceptions, less positive mood, and more negative mood while showing moderating effects between image type and positive mood. Findings suggest that body positive images on social media contribute to positive affffective responses, where social comparison can be a key to understanding the underlying mechanism.