Effect of chlorpromazine (dopamine receptor antagonist) on pre-pubertal ovarian follicular development and onset of puberty were studied. Fifteen days old female rats were administered chlorpromazine (2.5 mg /kg body weight) daily for 21 days and appropriate controls were maintained. The onset of puberty in immature female rats was delayed following chlorpromazine treatment. There were significant increases in the body weight, ovary weight and diameter of the ovary of controls and treated group over the initial controls. Ovary of the initial controls consisted of primordial (type 2), primary (type 3a, 3b), pre-antral (type 4, 5a, 5b) and antral (type 6) follicles whereas, antral (type 7) and pre-ovulatory follicles (type 8) were not developed. Controls and treated group consisted of all types of follicles i.e. primordial to pre-ovulatory follicles. Primordial follicles were reduced in number significantly in the ovary of the controls and treated group when compared with the initial controls whereas there was no significant variation among the controls and the treated group. The mean number of primary, pre-antral and antral (type 6) follicles in the control and treated group increased significantly over the initial controls. However, there was a significant reduction in the mean number of these follicles in the treated group when compared to controls. The mean number of type 7 (antral) and type 8 (pre-ovulatory) follicles were reduced in the treated group when compared with controls. The number of atretic follicles of the primary, pre-antral and antral (type 6) follicles significantly increased in controls and treated group over the initial controls. When compared to controls the mean number of atretic follicles belonging to primary, pre-antral, antral (type 6 and 7) and pre-ovulatory category were significantly higher in treated group and the number of corpora lutea was significantly lower. The results indicate that chlorpromazine effect results in loss of follicles by atresia and delay the onset of puberty in immature female rats.