Abstract: In order to study the effect of ester structure of water-soluble polyester(WSP) sizes on sizing properties of polyester warp yarns and investigate the size recipe of WSP sizes,two kinds of WSP sizes with different ester structures were synthesized through choosing different diol monomers and a series of sizing experiments was carried out on pure polyester warp yarns with WSP size blended with acidified starch.The results show that ester chemical structure of WSP sizes has great effect on sizing properties,and the sizing properties of blended size are remarkably improved if WSP size taking glycol as ester structure unit is employed.Moreover,the properties of starch sizes for pure polyester warp yarns are obviously improved if WSP sizes are properly used and the weight percentage of WSP to the blended size is 20%.