Although It has been said that Special Olympics competition contributes significantly to the physical fitness and self-concept of mentally retarded participants, no experimental research has been reported on the Special Olympics program. The purpose of this study was to investigate changes in self-concept and cardiovascular endurance of mentally retarded youths after participating in a Special Olympics swim training program. One group (N = 25) participated in a 10-week Special Olympics swim training program, while the control group (N = 25) adhered to their normal daily living activities. The 9-Minute Run/Walk test yielded the data for measuring cardiovascular endurance, and the Piers and Harris Children’s Self-Concept Scale was selected to measure self-concept. Results of the analysis of variance for each test were significant. It was concluded from the findings of this study that participation of mentally retarded youth in a Special Olympics swim training program contributed to a significant increase in self-concept and cardiovascular endurance.