Abstract: The influences of copolymer composition on the adhesion of polyacrylic sizes to polyester/cotton yarn are investigated by an impregnated roving method for warp sizing.The adhesion is evaluated in terms of the maximum strength,breaking elongation and work to break of a slightly sized roving.The polyacrylic sizes investigated include biopolymer of P(AM-co-AA) and homopolymers of PAA and PAM.The polymeric sizes were prepared through the polymerization of their corresponding monomers by free radical initiator.It was found that the adhesion of the polymeric sizes to the fibers is strongly depends on the type and amount of the structural units incorporated into the copolymer chains.The adhesion of the biopolymer sizes with appropriate ratio of AM to AA units on the fibers is superior to the homopolymers of PAM and PAA.