Ultraviolet (UV)B irradiation induces the production of matrix metalloproteinases (MMPs) by activating cellular signaling transduction pathways, which are responsible for the degradation or synthesis inhibition of collagenous extracellular matrix in connective tissues, causing skin photoaging. Using the human skin fibroblast (HS68) cell line in the present study, we investigated the inhibitory effects of fucoidan on MMP-1 expression by various in vitro experiments and elucidated the pathways of inhibition. Pretreatment with fucoidan inhibited UVB-induced MMP-1 expression in a dose-dependent manner. Extracellular signal regulated kinase (ERK) activation was markedly inhibited by treatment with fucoidan, though JNK activation was very slightly affected by fucoidan. We also found that fucoidan pretreatment significantly reduced MMP-1 mRNA expression in comparison with UVB irradiation only. In conclusion, our results demonstrate that fucoidan can mainly inhibit UVB-induced MMP-1 expression by inhibiting the ERK pathways. Therefore, fucoidan might be used as a potential agent for the prevention and treatment of skin photoaging.