Mutant MA 2504 carrying gap1 and apf1 ( shr3 ) double mutations and mutant MA 2601 carrying gap1 and can1 double mutations were isolated from the homothallic wine yeast Saccharomyces cerevisiae OC-2. MA 2504 was unable to grow on proline, alanine, aspartate, glutamate, phenylalanine, or valine, and MA 2601 was unable to grow on arginine when these amino acids were added to the medium as the sole nitrogen source. This indicates that the uptake of these amino acids was deficient in the mutants. Fermentation of Koshu grape must by both mutants MA 2504 and MA 2601 was completed to dryness, with a slower fermentation rate than that of the wine yeast OC-2. Supplementing the must with diammonium hydrogenphosphate restored the fermentation rate. Wine produced using MA 2504 retained 985.7 mg/l of total amino acid from must initially containing 1184.1mg/l and no diammonium hydrogenphosphate supplement. This represents almost twice the level of 521.1 mg/l in wine produced by the wine yeast OC-2. Wine produced by MA 2601 contained 662.9 mg/l of the total amino acid. Similar results were also observed in wines made from must supplemented with diammonium hydrogenphosphate. These results indicate that the use of wine yeast mutants carrying gap1 and apf1 ( shr3 ) double mutations or gap/ and canl double mutations effectively improves the amino acid content in Koshu wine.