Pleurotus eous was cultivated on soybean straw for analyzing the nutritional content of mushroom fruiting bodies and spent mushroom straw (SMS). Results showed the maximum moisture (86.10 to 88.70 %), total carbohydrate (53.70 to 57.90 %), protein (23.00 to 26.50 %), fat (2.10 to 2.86 %), crude fibre (6.50 to 7.90 %) and ash (6.50 to 8.10 %) content in mushroom fruiting bodies. The mushroom spent straw showed an increase in protein (3.50 to 5.90 %), ash (7.40 to 9.30 %) and moisture (6.90 to 8.15 %) content while a decrease in pH (7.10 to 5.4o%), Crude fiber (40.30 to 23.00 %), total carbohydrates (80.10 to 52.50 %), lignin (29.80 to 12.50 %), cellulose (39.10 to 27.50 %), hemicellulose (21.80 to 08.70 %) and tannin (37.20 to 24.30 %) content as compare to soybean straw. During spawn run period, lignin degradation was faster and during fruiting bodies formation, lignin degradation was slowed down while degradation of cellulose and hemicellulose in straw was faster in rate during fruiting bodies formation.