ANINVESTIGATION concerning the bioconversion of an alkali-……..treated rice straw to single cell protein under fermentation conditions by Saccharomyces cerevisiae was done. The optimal environmental and nutritional conditions, which resulted in the highest protein production by S. cerevisiae can be summarized as following; incubation temperature, 30°C; incubation periods, 48 h; pH of 4.5; inoculum size 1 ml/100ml from a heavy spore suspension of 95x10⁷ Colony Forming Unit (CFU) /ml, 2 g % rice straw concentrations; NH₄H₂PO₄ as best nitrogen source; carbon source 2.5 g % of lactose. The highest yields of single cell protein were obtained under static condition. High contents of nutritional compounds such as protein, mineral, carbohydrate, lipid, vitamins and amino acids were determined in the produced yeast biomass. These results show that Saccharomyces cerevisiae could be suitable for single cell protein production from cheap waste products.