The subcellular distributions of Cu, Fe, Mn, Zn, Mg, Ca, Cd, Pb, Al, and As in Sargassum fusiforme were examined, in order to reveal the subcellular distribution characteristics of different elements and the mechanism of its special hyperaccumulation of As. The results indicated that Cu, Fe, Mn, Zn, Ca and Mg were mainly stored in the plant cell walls, yet their distributional patterns in cytoplasmic supernatant and cell organelles were different. The concentrations of Al, Cd and Pb in the cell walls were much higher than those in either cytoplasmic supernatant or cell organelles. However, the subcellular distributions of As showed a decreasing trend as: cytoplasmic supernatant (58%) >cell wall (26%-27%)>cell organelles (15%-16%), indicating that the cytoplasmic supernatant was the main storage for As in S. fusiforme. The present study suggested that the isolation of As in cytoplasmic supernatant may be an important mechanism for accumulation of As in S. fusiforme.