The protein quality of ten food products in including beef, bovine rumen and four meat products extended with soy proteins had been evaluated by rat feeding experiment; defatted freeze-dried whole egg served as a reference protein. Mean endogenous fecal and metabolic urinary nitrogen amounted to 1.01 and 1.11 mg/g food consumed, respectively. True protein digestibility and biological value of beef averaged 90.3% and 82.6%, respectively. The protein qualities of bovine rumen are quite similar to that of beef. Beef products extended with soy protein are quite inferior in their true protein digestibilities (81.4-84.6%) and biological value (68.8-76.0%) as compared to beef. The utilizable protein of extended meat fluctuated between 22.6-29.3% compared with a mean level of 70% in beef.