The purpose of this study was to identify the effects of endurance training on cardiorespiratory function in mentally retarded children. There were fourteen untrained middle school boys who were randomly selected and divided into 2 groups, exercise group (N=7) and non-exercise group (N=7). The method of endurance training in each exercise group was the soccer training. The average duration, frequency, and intensity of endureance training were three times a week, one hour a day, and a 62.7% heart rate. The heart rate responses to the treadmill running and the blood lactate concentration were measured before and after 12-week endurance tracing. The date were tested(p<.05) by paire t-test and t-test.