Abstract: In order to reduce PVA proportion in sizing solution used for pure cotton finer yarns,nanomodified size can be prepared by adding different kinds of inorganic nanoparticles according to different proportions into a size commonly used for finer cotton yarns,reducing PVA content accordingly.The viscosity,adhesion,penetrating and covering effects as well as the completeness of the size film of the nanomodified size were tested.Optical microscope Olmpus BX-51 was used to examine the conventional and nanomodified sizes and the acting principle of modifying effect of nanoparticles was analyzed.The results indicated that addition of inorganic nanoparticles could reduce the viscosity of the size,enhance its adhesion,and improve the penetrating and covering effects and the completeness of the size film.A structure of net-like honeycomb was seen and the nanoparticle molecules were distributed at the juncture as observed on the fiber sized by nanomodified size,and it demonstrated that its mixing effect was improved.