Glycolic acid, an alpha-hydroxy acid derived from fruit and milk sugars, has been commonly used as a cosmetic ingredient since it was known to have photo-protective and anti-inflammatory effects, and anti-oxidant effect in UV-irradiated skin. However, little has been known about the functional role of glycolic acid on UV-induced skin tumorigenesis. We previously found that glycolic acid inhibited UV-induced skin tumor development in hairless mouse. In this study we investigated anti-tumor promoting mechanism of glycolic acid on the UV-induced skin tumor development. The ability of glycolic acid to inhibit the UVB-induced cytotoxicity, apoptosis and expression of apoptosis-regulatory genes (p53 and p21) was examined. We also investigated whether glycolic acid could inhibit UVB-induced alternation of cell cycle, c-fos expression and activation of transcription factor AP-1 in cultured immortalized human keratinocyte HaCaT cells. Glycolic acid treatment attenuated the UVB-induced cell cytotoxicity as well as apoptosis. Glycolic acid also inhibited the UVB-induced expression of c-fos and the activation of transcription factor AP-1, and inhibited mRNA levels of apoptosis-regulatory gene (p53 and p21). These results suggest that glycolic acid may exert the inhibitory effect on the UVB-induced skin tumor development by blocking the UVB-induced of apoptosis and cytotoxicity through inhibition of c-fos expression and activation of AP-1 in addition to the inhibition of p53-p2l response pathway.