In order to prepare its powder type, physico-chemical properties of malea-ted rosin size have been determined. Experiments show that the density and surface tension of rosin size varies slightly when temperature changes; the higher the temperature and water content increase, the lower the viscosity of ma-leated rosin size decreases; and specific heat drops as temperature rises. Experiments also indicate that when atmospheric temperature is 150~180癈 and the linear velocity of the centrifugal wheel is greater than 85 m/sec, sizing effects of the powder type are just the same as those of the paste type, as the same degree of sizing is employed. The diameters of the particles in emulsion of both powder and paste size are similar under a electron-microscope.