Abstract: 【Objective】To clarify the antitumor activity of polysaccharides from the Morinda citrifolia L. fruit，and to provide reference basis for the in-depth study of polysaccharide biological activity in M. citrifolia fruit and its development and application.【Method】The cytotoxicity of crude and purified polysaccharides of M. citrifolia fruit on normal colon epithelial cells was detected by thiazole blue colorimetry（MTT）assay. Then，the effects of polysaccharides on the proliferation and growth of human colon cancer cells SW620 and HCT-116，cervical cancer cell Hela and liver cancer cell QGY-7703 were evaluated，and the antitumor activity in vitro of purified polysaccharide was assessed by the frequencies of apoptosis and necrosis of cancer cells.【Result】The polysaccharides of M. citrifolia fruit were non-toxic，and crude polysaccharide at low concentrations（62.5-125 μg/mL）or purified polysaccharide at high concentrations（125-2000 μg/mL） had promoting effect on the proliferation of human normal colon epithelial cells. Polysaccharide from M. citrifolia fruit showed the strongest inhibitory effect on cervical cancer cell Hela，with both crude and purified polysaccharide significantly inhibiting the growth of cervical cancer cell Hela at the concentration range of 125-2000 μg/mL（P<0.05，the same below），with semi-inhibitory concentration（IC₅₀）of 542.80 and 1546.00 μg/mL. The polysaccharide of M. citrifolia fruit also had strong inhibitory effect on the proliferation and growth of colon cancer cell HCT-116，but had no obvious inhibitory effect on the proliferation of liver cancer cell QGY-7703. At a concentration of 1000 μg/mL，the crude polysaccharide of M. citrifolia fruit had the strongest inhibitory effect on colon cancer cells HCT-116 and cervical cancer cells Hela，the cell proliferation rates were 78.11% and 81.85% respectively. The purified polysaccharide at a concentration of 2000 μg/mL showed the strongest inhibitory effect on colon cancer cells HCT-116 and cervical cancer cells Hela，with cell proliferation rates of 57.05% and 68.64%. The growth inhibitory ability of purified polysaccharide on cancer cells was higher than that of crude polysaccharide. The purified polysaccharide had significant effect on the apoptosis and necrosis frequency of colon cancer cell HCT-116 and cervical cancer cell Hela，and the necrosis frequency of the both cancer cells increased with the increase of purified polysaccharide concentration，reaching a peak value at 2000 μg/mL，with the necrosis frequency of 2.83% and 6.75%.【Conclusion】The polysaccharide from M. citrifolia fruit has good activity of antitumor，and the purified polysaccharide shows much stronger antitumor activity than the crude polysaccharides.