Grape must was fermented by a mixed culture of Saccharomyces cerevisiae W-3 (a wine yeast) and Issatchenkia orientalis KMBL 5774 (a malic acid-degrading yeast). Co-fermentation with 1:1 (v/v) inoculum ratio of W-3 and KMBL 5774 decreased malic acid to 0.33 mg/ml from 1.1 mg ml with W-3 alone. Ethanol production was the same in both cases (7.8%, v/v). Acetaldehyde, 1-propanol, 2-butanol and isoamyl alcohol all decreased, with an increase in methanol, in the co-fermented wine. Sensory evaluation showed a higher score in the wine fermented with 1:1 (v/v) inoculum ratio than those obtained by 4:1 (v/v) inoculum ratio or W-3 alone.