Objective · To investigate effect of fucoidan on autophagy, migration and invasion in human multiple myeloma U266 cells. Methods · The U266 cells treated with fucoidan were cultured in vitro. The formation of autophagosomes was observed by transmission electron microscopy (TEM).Transwell assay was used to evaluate the effect of fucoidan on migratory and invasive abilities of U266 cells. The protein levels of LC3-Ⅱ/LC3-Ⅰ, Beclin-1, P62, MMP9, CXCR4, p-AKT/T-AKT, p-mTOR/T-mTOR were detected by Western blotting. MMP9 concentration in the culture medium was examined by ELISA. Results · ①Autophagosomes increased in fucoidan-treated cells compared with control group under TEM. ② Migratory and invasive abilities were inhibited by fucoidan in a dose-dependent manner, which were suppressed by chloroquine. ③Western blotting demonstrated that expression of LC3-Ⅱ/LC3-Ⅰ, Beclin-1 and MMP9 increased in fucoidan-treated cells, while P62, CXCR4, p-AKT/T-AKT and p-mTOR/T-mTOR decreased compared with control group. ④The result of ELISA showed that MMP9 concentration in the culture medium of fucoidan-treated cells significantly decreased. Conclusion · Fucoidan induces autophagy and inhibits migration and invasion in U266 cells.