The purpose of this study was to determine the effects of water exercises and swimming on physical fitness of children with mental retardation. Nine trainable and 7 educable male children (n = 16) were recruited from a rehabilitation center. The mean ages of the groups were 12.22 +/- 0.49 and 14.71 +/- 0.52 years, respectively. Training program was applied for 10-week, two times a week for 40 minute each session. Pre- and post-tests measurements were taken for cardiovascular endurance, muscle endurance, speed, static balance, and agility Results showed that both groups improved significantly (p<0.05) in all dependent variables. Water exercises and swimming appear to be a viable and effective way to improve physical fitness capacity of the children with mental retardation.