1,25-dihydroxy vitamin D3(VD3),an active form of Vitamin D,is photosynthesized in the skin of vertebrates in response to solar ultraviolet B radiation(UV-B).VD3 deficiency can cause health problems such as immune disease,metabolic disease,and bone disorders.It has also been demonstrated that VD3 is involved in reproductive functions.Female sex hormones such as estrogen and progesterone are biosynthesized mainly in ovarian granulosa cells as the ovarian follicle develops.The functions of sex hormones include regulation of the estrus cycle and puberty as well as maintenance of pregnancy in females.In this study,we isolated granulosa cells from porcine ovaries and cultured them for experiments.To examine the effects of VD3 on ovarian granulosa cells,the mRNA and protein levels of genes were analyzed by Real-time PCR and Western blotting assay.Production of progesterone from granulosa cells was also measured by ELISA assay.As a result,transcriptional and translational regulation of progesterone biosynthesis-related genes in granulosa cells was significantly altered by VD3.Furthermore,progesterone concentrations in porcine granulosa cell-cultured media decreased in response to VD3.These results show that VD3 was a strong regulator of sex steroid hormone production in porcine granulosa cells,suggesting that vitamin D deficiency may result in inappropriate sexual development of industrial animals and eventually economic loss. 1,25-dihydroxy vitamin D3 (VD3), an active form of Vitamin D, is photosynthesized in the skin of vertebrates in response to solar ultraviolet B radiation (UV-B) .VD3 deficiency can cause health problems such as immune disease, metabolic disease, and bone disorders. It has also been demonstrated that VD3 is involved in reproductive functions. Female sex hormones such as estrogen and progesterone are biosynthesized mainly in ovarian granulosa cells as the ovarian follicle develops.The functions of sex hormones include regulation of the estrus cycle and puberty as well as maintenance of pregnancy in females. In this study, we isolated granulosa cells from porcine ovaries and cultured them for experiments. To examine the effects of VD3 on ovarian granulosa cells, the mRNA and protein levels of genes were analyzed by Real-time PCR and Western blotting assay. Production of progesterone from granulosa cells was also measured by ELISA assay. As a result, transcriptional and translational regulation of progest erone biosynthesis-related genes in granulosa cells was significantly altered by VD3.Furthermore, progesterone concentrations in porcine granulosa cell-cultured media decreased in response to VD3. These results show that VD3 was a strong regulator of sex steroid hormone production in porcine granulosa cells, suggests that vitamin D deficiency may result in inappropriate sexual development of industrial animals and eventually economic loss.