Background: Information regarding how the Special Olympics programs affect volunteers' self-esteem and attitudes towards individuals with intellectual disability (ID) is limited. We conducted a quasi-experimental study to address this gap. Method: The intervention group participants (n = 120) were Chinese volunteers for the Special Olympics Eunice Kennedy Shriver University Day. They were asked to attend a pre-service training program and provide a half-day service. Results were compared with a control group (n = 123). Results: Our findings showed that the volunteers' self-esteem and attitudes immediately improved after intervention. In addition, change in participants' self-esteem contributed to their positive attitude change. Conclusions: The Special Olympics may provide an avenue for promoting the volunteers' self-esteem and attitudes regarding inclusion towards individuals with ID. Future research should include follow-up tests to examine the lasting effects of intervention.