Isolation of sake-yeast mutants having high ability to produce isoamyl acetate and ethyl caproate, which are known to be the essential flavor components of sake, was carried out. As the result, mutants of sake-yeast having high ester-producing ability could be isolated at high frequency by using CAN medium containing L-canavanine and AP medium containing aniline blue and ponceau 2R in conbination. The use of mutants isolated was efficient to make a sake containing abundant flavor compounds.