A novel sulfated polysaccharide SRBPS2a with anti-tumor activity was derived from defatted rice bran by chlorosulfonic acid-pyridine(CSA-Pyr) method.The average molecular weight of SRBPS2a was 3.5×105 u and the degree of sulfation(DS) was 1.29.The Fourier-Transform Infrared Spectra(FT-IR) and 13C NMR spectroscopy analysis revealed that SRBPS2a was mainly consist of β-(1→3)-D-galactopyranosyl residues,the sulfate substitution site was on C-2 and C-4 while the side chains were cut off during the sulfated reaction.Furthermore,SRBPS2a exhibited evident growth inhibition on mouse mammary tumor EMT-6 cells both in vitro and in vivo.