Continuous fermentation using the industrial saccharomyces cerevisiae diploid strain ww was carried out under acidic or high-teinperature conditions to achieve acid-or thermo-toierant mutants. Mutants isolated at PH 2. 5 and 41 °c _---showed improved growth and fermentation ability under acidic and elevated temperature conditions. Haploid strains WW17A1 and WW17A4 obtained from the mutated diploid strain WW17A showed better growth and 4.5-6. 5%higher ethanol yieldas at ph2.7 than the original strains.