Studies during the past few years have indicated an inhibitory effect of green tea or tea polyphenols on tumorigenesis in animal and even in human. The purpose of this study was to observe the possible effects of tea polyphenols on skin cell growth and on apoptosis in rat primary cultured keratinocytes and fibroblasts. The release of a cell plasma enzyme (LDH), lipid peroxidation products (MDA production), and GSH_Px (glutathione peroxidase) into the medium in cultured cells was determined after treatment with tea polyphenols in a primary culture of skin cells. The percentage of cells in each cell cycle phase and in apoptosis were assayed by flow cytometry (FCM). Tea polyphenols may have a beneficial effect on skin cells at concentrations from 0.05% to 0.1%, showing a dose_dependent decrease in LDH, MDA (malondialdehyde) production, and a significant dose_dependent increase in GSH_Px and cell number. These effects were more obvious after exposure for 24 h than after 12 h. The results indicate that tea polyphenols may stabilize and protect the cell membrane against the release of cell plasma enzyme LDH, and its anti_peroxidation effect is also important for cell growth. FCM analysis revealed that treatment with 0.01% to 0.1% tea polyphenols decreased the percentage of cells in the G 1/G 0 (quiescent) phase from 81.32% to 74.38%, and increased the percentage of cells in S and G-2/M phase from 9.87% to 15.26%, and from 6.51% to 10.36%, respectively. Tea polyphenols also increased the value of PI (proliferation index) from 18.17 to 25.62. At the same time it decreased the percentage of apoptosis from 27.10% to 17.97%, which indicates that green tea stimulates cell growth and inhibits the occurrence of apoptosis. Our results indicate that tea polyphenols are effective anti_oxidants and also inhibit apoptosis, which may improve the proliferative capacity of primary skin cells in vitro. Studies have the past few few years have indicated an inhibitory effect of green tea or tea polyphenols on tumorigenesis in animal and even in human. The purpose of this study was to observe the possible effects of tea polyphenols on skin cell growth and on apoptosis in rat primary The cultured keratinocytes and fibroblasts. The release of a cell plasma enzyme (LDH), lipid peroxidation products (MDA production), and GSH_Px (glutathione peroxidase) into the medium in cultured cells was determined after treatment with tea polyphenols in a primary culture of skin cells . The percentage of cells in each cell cycle phase and in apoptosis were assayed by flow cytometry (FCM). Tea polyphenols may have a beneficial effect on skin cells at concentrations from 0.05% to 0.1%, showing a dose_dependent decrease in LDH, MDA ( Malondialdehyde) production, and a significant dose_dependent increase in GSH_Px and cell number. These effects were more obviously after exposure for 24 h than after 12 h. The results i Ndicate that tea polyphenols may stabilize and protect the cell membrane against the release of cell plasma enzyme LDH, and its anti_peroxidation effect is also important for cell growth. FCM analysis revealed that treatment with 0.01% to 0.1% tea polyphenols decreased the percentage of cells in The G 1/G 0 (quiescent) phase from 81.32% to 74.38%, and increased the percentage of cells in S and G-2/M phase from 9.87% to 15.26%, and from 6.51% to 10.36%, respectively Tea polyphenols also increased the value of PI (proliferation index) from 18.17 to 25.62. At the same time it decreased the percentage of apoptosis from 27.10% to 17.97%, which indicates that green tea stimulates cell growth and inhibits the occurrence of apoptosis. Our results indicate that tea polyphenols are effective anti_oxidants and also sustain apoptosis, which may improve the proliferative capacity of primary skin cells in vitro.