Abstract: Through maleate esterification of starch to introduce carbon-carbon double bonds onto starch,the graft copolymerization of acrylic acid with the above esterified starch was carried out in order to enhance the graft efficiency and improve the sizing properties of the grafted starch in warp sizing.The results indicated that the esterification can raise grafting efficiency by 10%～30% when the degree of substitution of starch maleate is in a range of(0.013 6) to (0.041 2).And the esterification also increases the adhesion of the grafted starch to fibers and improves its film property significantly.The experiment manifested that the modification extent was in a range of DS=(0.013 6)～(0.020 6.)