The study aimed to investigate the effects of FSH and eCG on the ovarian and follicular development, expression levels of FSHR and caspase-9 of ovaries in vivo. One hundred and five prepuberty mice were allocated into FSH-1, FSH-2, FSH-3, eCG-1, eCG-2, eCG-3 groups and control group (CG). Mice in FSH-1, FSH-2 and FSH-3 were intramuscularly injected with 5, 10 and 20 IU FSH twice (on day 0 and 4), respectively. Mice in eCG-1, eCG-2 and eCG-3 were intraperitoneally injected with 10, 20 and 40 IU eCG on day 0 and 4. Mice in the CG were injected with 0.5 ml normal saline on day 0 and 4. Left and right ovaries of each mouse were dissected aseptically on days 7, 14 and 21, respectively. The results showed that on days 14 and 21 the ovarian sizes and follicle numbers of FSH-3 and eCG-3 groups were greater than CG (P<0.05). FSHR mRNA of FSH-2 and eCG-1 were higher than CG on days 14 and 21 (P<0.05). FSHR proteins of FSH-3 were higher than CG on days 14 and 21 (P<0.05). Caspase-9 mRNA in FSH and eCG groups was less than CG. There were positive correlations between follicle numbers and FSH and eCG doses. FSHR protein expressions had positive correlations between ovarian weights and sizes of ovary and follicle numbers (r=0.971, P<0.05) in FSH-treated mice. Serum FSH concentrations of FSH-2, FSH-3, eCG-2 and eCG-3 groups were greater than that of CG. In conclusion, eCG and FSH promoted the ovarian development, follicle genesis, FSH secretion, FSHR mRNA and protein expressions in ovaries of mice. FSH and eCG inhibited the expression of ovarian caspase-9 mRNA.