Three new steroid biglycosides, plancisides A-C (1-3), were isolated from the ethanolic extract of the starfish Acanthaster planci. The structures of 1-3 were determined by extensive NMR and ESI-MS techniques, as (24S)-28-O-[β-D-galactofuranosyl-(1-->5)-α-L-arabinofuranosyl]-24-methyl-5α-cholestane-3β, 4β, 6α, 8, 15α,16α, 28-heptol (1), (24S)-28-O-[α-L-fucopyranosyl-(1 --> 2)-3-O-methy-β-D-xylopyranosy]-24-methy-5α-cholestane-3β, 4β,6α,8,15β,16β,28- heptol (2) and (24S)-28-O-[2,4-di-O-methyl-β-D-xylopyranosyl-(1 --> 2)-α-L-arabinofuranosyl]-24-methyl-5α-cholestane-3β,4β,6α,8,15β,16β,28-heptol 6-O-sulfate (3), respectively. Compound 2 is the first steroid glycoside containing an α-fucopyranose unit found from starfish. Compound 1 slightly inhibits cell proliferation of HCT-116, T-47D, and RPMI-7951 cancer cell lines, but has no effect on colony formation of these cells in a soft agar clonogenic assay.