Abstract: Objective To extract the crude polysaccha rides from water-caltrop and to study their antitum or effect in vitro.Methods Ethanol fractionation method was used to separate crude polysaccharides from water-caltrop.MTT method was used to evaluate the antitum or effect of crude polysaccha rides in vitro.Flow cytome try method was used to detect the apoptosis of U251 cells induced by the crude polysaccha ride.Results Three kinds of polysaccha ride compounds were obtained from the water-caltrop.The results of MTT assay showed that different concentration(7.81,15.63,31.25,62.50 and 125.00μg/mL)of the crude polysaccha rides could significantly inhibit the prolife ration of Hela and U251 cells in a dosedependent manner and induce the cell apoptosis.The number of two kind cells gradually decreased with the increasing of concentration of the crude polysaccha rides.Conclusion The results proved that crude polysaccharide could inhibit the Hela and U251 cells proliferation and induce U251 cell apoptosis.