Protein nutrition is important for human health because its deficiency leads to major public health problems such as Protein Energy Malnutrition. Soybean an excellent and cheap source of high quality protein has been introduced into the Western Kenya and other developing countries for improved health and food security, but end use qualities may reduce its utilization. The main objective of this study was to evaluate the protein nutritional quality of four soybean varieties grown in Western Kenya. Protein quality was determined using male weanling albino rats for the indices of net protein retention, food efficiency, apparent and true protein digestibilities and faecal weight. Soybean amino acid efficiency was evaluated using Protein digestibility corrected amino acid score (PDCAAS). Soybean diet SB 132 had the highest protein nutritional quality with the best protein retention of 6.29 g, Apparent Protein digestibility of 89.13%, True Protein Digestibility of 96.48%, weight gain of 5.50 g and a Net Protein Retention Ratio of 4.70. All the four soybean varieties had high amino acid profiles with a Protein digestibility Corrected Amino Acid Score of 1.0. Soybean variety SB 132 is the most superior in digestibility and the study recommends its promotion as a food crop in Western Kenya and other developing countries for the management of Protein Energy Malnutrition and for food security.