Industrial strains of Saccharomyces cerevisiae are generally incompetent for mating with others and hard to sporulate. Physical and functional analyses of Kyokai no. 7, a typical sake yeast, revealed that it has functional a and alpha mating-type genes and the mating incompetency has the regular non-mater phenotype due to alpha2 and a1-alpha2 repression. An effective selection method for isolation of mating-competent mutants of this strain was developed using plasmids bearing fused genes, STE6p-PHO5 and MFalpha1p-PHO5, consisting of the promoter of STE6, an a-specific gene, and MFalpha1, an alpha-specific gene, respectively, connected to the coding region of PHO5 encoding repressible acid phosphatase. Mating-competent mutants having the a or alpha mating type were selected by detection of repressible acid phosphatase activity by specific staining of colonies. This method was applied successfully to two other sake yeasts. Hybrid yeast strains superior for sake making were constructed by crossing these mating-competent derivatives.