Background Nitic oxide (NO) has been implicated in the pathogenesis of various inflammatory diseases, including sunburn and pigmentation induced by ultraviolet irradiation. Epigallocatechin-3-gallate (EGCG) is the major effective component in green tea and can protect skin from ultraviolet-induced damage. The purpose of this study was to investigate the protective mechanisms of EGCG on inducible nitric oxide synthase (iNOS) expression and NO generation by ultraviolet B (UVB) irradiation in HaCaT cells. Methods HaCaT cells were irradiated with UVB 30 mJ/cm2 and pretreated with EGCG at varying concentrations. The iNOS mRNA was detected by reverse transcriptase polymerase chain reaction (RT-PCR) and NO production was quantified by spectrophotometric method. The expression of NF-κB P65 was measured by immunofluorescence cytochemistry staining. Results The expression of iNOS mRNA and generation of NO in HaCaT cells were increased by UVB irradiation. EGCG down regulated the UVB-induced iNOS mRNA synthesis and NO generation in a dose dependent manner. The UVB-induced activation and translocation of NF-κB were also down regulated by EGCG treatment in HaCaT cells (P<0.01). Conclusions Green tea derived-EGCG can inhibit and down regulate the UVB-induced activation and translocation of NF-κB, expression of iNOS mRNA and generation of NO respectively, indicating EGCG may play a protective role from UVB-induced skin damage. Epidermallocatechin-3-gallate (EGCG) is the major effective component in green tea and can protect skin from ultraviolet-induced Damage. The purpose of this study was to investigate the protective mechanisms of EGCG on inducible nitric oxide synthase (iNOS) expression and NO generation by ultraviolet B (UVB) irradiation in HaCaT cells. Methods HaCaT cells were irradiated with UVB 30 mJ/cm2 and The iNOS mRNA was detected by reverse transcriptase polymerase chain reaction (RT-PCR) and NO production was quantified by spectrophotometric method. The expression of NF-κB P65 was measured by immunofluorescence cytochemistry staining. Results The expression of The iNOS mRNA and generation of NO in HaCaT cells were increased by UVB irradiation. EGCG down regulated the UVB-induced iNOS The mRNA synthesis and NO generation in a dose dependent manner. The UVB-induced activation and translocation of NF-κB were also down regulated by EGCG treatment in HaCaT cells (P<0.01). Conclusions Green tea derived-EGCG can inhibit and down regulate the UVB-induced activation and translocation of NF-κB, expression of iNOS mRNA and generation of NO respectively, indicating EGCG may play a protective role from UVB-induced skin damage.