In summary, our results demonstrated that soy isoflavone extract Fraction 3 from soybean cake could prevent human keratinocyte apoptosis, attenuate the level of erythema and TEWL, reduce the epidermal thickness and increase the catalase activity and inhibit COX-2 and PCNA expression in response to UVB exposure. This evidence concerns the gene PTGS2 and Erythema.