Ethanol production from rice straw by simultaneous saccharification and fermentation (SSF) with Mucor indicus, Rhizopus oryzae, and Saccharomyces cerevisiae was investigated and compared with pure cellulose, Avicel, as a reference. The straw was pretreated with dilute-acid hydrolysis. The SSF experiments were carried out aerobically and anaerobically at 38 °C, 50 g/l dry matter (DM) solid substrate concentration and 15 or 30 filter paper unit (FPU)/g DM of a commercial cellulase. The experiments were ended after 7 days, while an average of 2–3 days were usually enough to achieve the maximum ethanol yield. All the strains were able to produce ethanol from the pretreated rice straw with an overall yield of 40–74% of the maximum theoretical SSF yield, based on the glucan available in the solid substrate. R. oryzae had the best ethanol yield as 74% from rice straw followed by M. indicus with an overall yield of 68% with 15 FPU/g DM of cellulase. Glycerol was the main byproduct of the SSF by M. indicus and S. cerevisiae with yields 117 and 90 mg/g of equivalent glucose in the pretreated straw, respectively, while R. oryzae produced lactic acid as the major byproduct with yield 60 mg/g glucose equivalent in pretreated rice straw under anaerobic conditions.