Objectives: Numerous studies have linked experiences of appearance-related interpersonal rejection to body dissatisfaction (BD), though few experimental studies have been conducted. This study assessed causal effects of appearance-related social exclusion during an online Cyberball game on state BD as well as potential moderators of this association. Methods: Young Chinese adults (60 women, 37 men; age 20.08 ± 1.32 years) were asked to provide an image of themselves that would be sent to other players prior to a visual perception study involving Cyberball, a virtual ball-tossing game that is used to elicit temporary social exclusion effects. Participants completed a trait Fear of Negative Appearance Evaluation (FNAE) measure before or after engaging in the Cyberball task in addition to post-task state measures of BD and positive mood facets. Results: Participants randomly assigned to the social exclusion condition (i.e., receiving 2 of 30 possible throws) reported significantly higher post-Cyberball state BD and significant happiness/energy level/self-confidence deficits compared to peers in a social inclusion condition (i.e., receiving 12 out of 30 throws). A hierarchical regression analysis indicated social exclusion condition membership and trait FNAE elevations, but not their interaction, were significant predictors of higher state BD scores, independent of the impact of gender. Conclusions: Social exclusion experiences linked to physical appearance are a significant causal influence on increases in state BD and positive mood decrements among young Chinese adults.