A native polysaccharide (MCP2) was extracted and isolated from Momordica charantia. Four sulphated derivatives of MCP2 were prepared by chlorosulphonic acid method. The structures of the sulphated derivatives were characterised by FT-IR spectra. Depending on the reaction conditions, the sulphated derivatives showed different degree of substitution (DS) ranging from 0.56 to 1.10, and different weight-average molecular mass (Mw) ranging from 7.2 to 9.3 KDa. It implied the efficient substitution of hydroxyl groups in the polysaccharides by sulphated groups with degradation. The effects of the sulphated derivatives on inhibiting the growth of HepG2 cells and Hela cells in vitro were compared with taking non-modified MCP2 as control. The sulphated derivatives inhibited the growth of HepG2 cells and Hela cells in vitro significantly, which indicated that sulphated modification could enhance the anti-tumour activity of MCP2.