Abstract: In order to improve the usability of starch/polyvinyl alcohol (PVA) composite film in the application based on the films such as warp sizing in textile, the preparation of quaternized-maleated cornstarch (QMS) was performed by a method of two-step reaction. In terms of the tensile strength, the breaking elongation, the flex fatigue resistance, and the toughening law of modification level (the sum of quaternization level and maleation one) on QMS/PVA composite films was explored, and the effect of mass ratio of PVA to QMS on the toughness of QMS/PVA composite films was also investigated. It can be found that the tensile strength of QMS/PVA composite films reduces from 21.6 MPa to 14.8 MPa, and the breaking elongation and the number of bending of QMS/PVA composite film increase from 26.6% to 29.5% and from 4 348 cycles to 5 388 cycles when the modification level of QMS is 0.061. When the mass ratios of PVA to QMS changes from 0 to 100%, the elongation of QMS/PVA composite films rises from 3.35% to 43.9%, the number of bending increases from 2 128 cycles to 7889 cycles, and the strength decreases from 27.1 MPa to 12.1 MPa. These results suggest that the mass ratio is the index of actors that influences the toughness of QMS/PVA composite films. The suitable mass ratio is about 66.7% based on the film properties.