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Abstract Introduction: Evaluation of the quality of food proteins have a great importance because of its biological and economical asfects. However biological, microbiological, chemical and combined methods have been used and introduced for determining quality of Proteins. Among the exsisted methods, NPR, RNPR,TPD and PER have been suggested as appropriatie methods for determining quality of Proteins. This study has been conducted to evaluate of quality protein of soya, using the mentioned methods on the soya products in 2003. Materials & Methods: This experimental study has been made on 48 male wistar rats, aged 21-23 days under 6 food diet in boundles of 8 including 3 diet soya, Casein+Methionine and control (free Protein) in order to study RNPR and PER (The condition of studing RNPR and PER are the same with the exception that the duration of study on PER is 28 days without limitation of Protein intake) and 3 diet soya, Casein+Methionine and control for studing TPD. Period of study for NPR was 14 days. Protein intake, weight increase was determined for calculating NPR. Period of study for TPD was 9 days. Nitrogen intake and fecal Nitrogen were determined for calculating TPD. Protein intake and change in weight of animals were determined. Rata of NPR, RNPR, TPD and PER was evaluated by T- test. Results: Indicator of NPR was calculated 3.650.35 and 4.370.48 for soya and Casein+Methionin respectively (P<0.01) and RNPR=83. Indicator of TPD was calculated 83.232.5 and 93.452.22 for soya and Casein+Methionin respectively (P<0.0001). Indicator of PER was 2.280.35 and 3.040.24 for Soya and Casein+Methionin respectively (P<0.001). Conclusion: Soya protein as compared with Casein is of lower quality.