he sffects of photoperiod on the growth, developinent and reproduc-tion of Syrian hamsters were examined in this experiment. There were23=6 groups of male and female weaning liamsters reared seperately inthree light: dark photoperiod circumstances ( 16L: 8D, 12L, 12D, and 8L: 16D) .At 13 weeks from birth, the body weights of shortlighting group( 8L: 16D ) male animals were significantly(P<0.05 ) higher than those ofthe other groups( i.e. 16L: SD and 12L: 12D ) . At 9 weeks from birth.the body weights of long-lighting group ( 16L: SD ) female animals weresignificantly ( P<0.01 ) higher than those of the other groups(i.e.12L,12D and 8L: 16D) . It is considered that the higlier daily intake mightbe one of the causes for long-ligliting female animals having greater bodyweights. With the increase of lighting time the weights of testes,epididy-mides and adrenals of male animals and the weights of ovaria, uteriand adrenals of female animals also presented a trend of incrsase. Long-lighting condition is beneficial to the normal estrogenicity and reproduc-tion of feinale hamsters. 16 hours lighting exposure each day is reasonablefor botli male and female breeding hamsters.