Mental retardation (MR) plays an important role in a child’s physical fitness development as well as his or her cognitive abilities during life. Most literature on the subject states that mentally retarded children have a poor level of physical fitness compared to their non-disabled peers. (Horvat & Franklin, 2001; Pitetti et al., 2001).The therapeutic effects of swimming and aquatic exercises on physical fitness and well-being have been recognized for people with disabilities (Broach & Datillo, 1996; Lepore, 2000; McHugh, 1995; Ruoti et. al., 1997). Furthermore, aquatic exercises are highly recommended for children as a recreational sport activity (Sherrill, 1986). Although there have been studies about the effects of swimming exercises on children without disabilities, there had been no research about these effects on children with MR. Therefore, the purpose of this study was to evaluate the effects of a ten-week aquatic exercise and swimming program on the physical fitness levels of mentally retarded children. The study included nine trainable and seven educable children from the Ankara Shelter and Rehabilitation Center. The mean age of the children was 12.22±0.49 years in the trainable group (n=9) and 14.71±0.52 years in the educable group (n=7). The training program consisted of a 40-minute swimming and water exercise session, twice weekly for ten weeks. The study included both a pre-test and post-test measuring the cardiovascular endurance, muscular endurance, speed, static balance, and agility of the subjects (Vannier & Faith, 1975). The Mann Whitney U test was used to compare the two groups and the Wilcoxon Matched Pairs Signed-Rank test was used within each group. A comparison between the results of the pre-test and post-test showed that both groups improved significantly (p<0.05) in all measured areas. Consequently, swimming and water exercise appear to be viable and effective ways to improve the physical fitness capacity of mentally retarded children. The results of the study show that these exercises have a noticeable effect on the subjects’ physical fitness. Therefore, children with MR should be encouraged to participate in water and swimming exercises as well as other sport activities on a regular basis. It is important to emphasize that this study has several limitations, such as the characteristics of the participants, intervention, tests, and the measurements that were applied. Therefore, further studies should address the effects of different settings and types of physical activities on the physical fitness of children with MR. Keyword(s): adapted physical activity, aquatics, exercise/fitness