High protein beverage of cow-soy milk was prepared by mixing the soymilk and commercial homogenized cow milk in the various ratios. Effect of heat treatment, pH and addition of calcium and sucrose was studied on the water-soluble nitrogen of cow-soy milk The heat-treated soymilk at 10$0^{circ}C$ were centrifuged at the range of 830~29,900xg for 30 min and 11,200xg was found to be proper for determination of the degree of protein denaturation by centrifugal method. When soymilk was heated at 70~10$0^{circ}C$ for 30~240 min, soluble nitrogen (QA SN) in supernatant of protein was decreased to 78.0~56.8% due to protein denaturation. Most of heat denaturation of protein was found to be occurred during Initial heating 10$0^{circ}C$ for all mixed cow-soy milk. The sedimentation of SN was maximum at pH 4.0 In the range of pH 3~8. Addition of sucrose affected little on oASN while calcium addition reduced %SN significantly to approx. 55% for soymilk(100%). The effect of Ca was less as the ratio of cow milk increased.