Ultraviolet (UV) radiation damages human skin and causes skin diseases such as epidermal hyperplasia, sunburn, inflammatory responses and photoaging. Photoaging is associated with upregulated matrix metalloproteinase (MMP) expression and downregulated collagen synthesis. Fucosterol, which is isolated from marine brown algae, has been reported to possess antioxidant and anticancer activities; however, its effects on photoaging are unknown. This study assessed the effects of fucosterol on photoaging and investigated its mechanisms of action in UV-irradiated immortalized human keratinocytes (HaCaT) by enzyme-linked immunosorbent assay, semi-quantitative reverse transcription-polymerase chain reaction, Western blot analysis and 2′,7′-dichlorofluorescein diacetate assay. Our results showed that fucosterol attenuated UV-induced MMP and inflammatory cytokine expression by deactivating mitogen-activated protein kinases (MAPKs) induced by reactive oxygen species. Fucosterol also increased type-I procollagen and antioxidant enzyme expression. Taken together, fucosterol regulates the expression of MMPs and type-I procollagen in UV-irradiated HaCaT by modulating MAPK, suggesting it as a potential candidate for prevention and treatment of skin aging.