Methanol and aqueous extracts of Styrax japonica Sieb. et Zucc used traditionally for the treatments of skin elastic materials were screened in vitro for the gelatinases B inhibitor actions. Erythrodiol-3-acetate (E) from the stem barks of S. japonica showed significant gelatinase B inhibition in human keratinocyte cells caused by ultraviolet irradiation. Here we investigated the effect of E, which was isolated from S. japonica on UV-induced premature skin aging. We studied the effect of E on UV-induced gelatinase B expression in an immortalized human keratinocyte cell line, in vitro. Acute UV irradiation induced gelatinase B expression at the protein levels and E suppressed this UV-induced gelatinase B expression in a dose-dependent manner. Taken together, these results show that E can prevent the harmful effects of UV that lead to skin aging or skin cancer. Therefore, we suggest that E should be viewed as a potential therapeutic agent for preventing and/or treating premature skin aging.