The purpose of this study was to evaluate the effect of 6 weeks of core stability training on the balance of mentally retarded. Our subjects included 31 male mentally retarded students in two groups (control, 14 patients with a mean age of 11/07±3/02years, height 152±7/86cm) and (17experimental group with a mean age 11/23 ± 1/95years, height 147±7/07cm) and were A group of healthy students (15 subject with mean age 11/53±./516years,high 155± 4/77cm) of the random pare selected. The training program of experimental group that includes core stability exercises for 6 weeks, 3 times a week in the first two weeks experimental group performed exercise the 2 sets with 5 repetitions and two the second week of 2 sets with 10 repetitions and for evaluate used the dynamic balance Y test (r= 91%).From independent T-test was used to compare pre and post-test and one-way ANOVA test was used in order to compare inter-group differences.)p≤0.05(.Results showed that dynamic balance was significant in poster medial and on the whole, there was a significant difference between groups in posterior lateral and posterior medial directions. On base of the results of this research the core stability exercises can be performed for mental retarded and healthy people by coaches and teachers.