Isoamyl alcohol is an important flavor component of yeast-fermented alcoholic beverages. To identify the enzyme and gene involved in the decarboxylation of alpha -ketoisocaproate (alpha -KIC) for isoamyl alcohol formation, the enzyme was partially purified and analyzed by mass spectrometry. The pyruvate decarboxylase encoded by the PDC1 gene was considered a likely candidate enzyme. Genetic analysis showed that the activity of alpha -KIC decarboxylase and production of isoamyl alcohol partially decreased in a pdc1 null mutant and increased in a transformant with a multi-copy plasmid carrying the PDC1 gene. These results indicate that pyruvate decarboxylase encoded by the PDC1 gene contributes, at least partially, to the decarboxylation of alpha -KIC for isoamyl alcohol formation.