Abstract: Rapid Visco Analyzer (RVA) and X-ray diffraction (XRD) were used to study the effect of different amylopectin contents on the pasting behavior and crystallinity of corn starch for warp size. The results indicated that there was a tendency, for the mixtures of corn starch and amylopectin with increase of amylopectin content, to decrease the peak viscosity, valley viscosity, final viscosity, the values of breackdown and setback, and the pasting time. It means that addition of amylopectin was good for starch pasting and for stablity of the starch paste. Meanwhile, the crystallinity of the mixed starch films decreased and the crystallite dimension inceased with increase of amylopectin content.