The cytogenic study included 20 mentally retarded children within the age group of 1 to 16 years, were evaluated for numerical chromosomal abnormalities. Out of 20 subjects, the first 11 samples were taken from the children of the school of the Mentally Retarded People, university road, Rajkot and the rest 09 samples were collected from the patients visited to Psychiatric OPD at the Government Civil Hospital, Rajkot. 15% female subject while 85% male subjects were evaluated for the present study. The selection criteria were children of the age between 1 and 16 years and the confirmation of mental retardation. The severity of category of mental retardation has not been focused. Chromosome preparation from peripheral blood cultures was done using standard techniques and cytogenic analysis was performed using GTG-Banding technique. 10% Karyotype were observed with numerical chromosomal abnormalities and that is Trisomy of 21st pair of chromosome. The study concluded that chromosomal abnormalities are thought to be the most common cause of mental retardation. However, apart from a few selected types with typical aneuploidy, like Down’s syndrome, the frequency of detectable chromosomal abnormalities in association with idiopathic mental retardation is very low.