A Candida antarctica lipase B (CALB)-displaying yeast whole-cell biocatalyst was constructed with the integration of the CALB cell-surface display expression cassette in the yeast genome and cell fusion by mating. Lipase hydrolytic activity of the yeast whole-cell biocatalyst subsequently increased, in both a- and alpha-type yeast cells, with the number of copies of the CALB cell-surface display expression cassette introduced, and reached 43.6 and 32.2 U/g-dry cell at 168 h cultivation, respectively. The lipase hydrolytic activity of whole cells in diploid yeast cells containing eight copies of the CALB cell-surface expression cassette reached 117 U/g-dry cell, and this value is approximately ninefold higher than that of the previously reported haploid CALB cell-surface displaying yeast using a multi-copy plasmid (Tanino et al. Appl. Microbial Biotechnol 75:1319-1325, 2007). This improved novel CALB-displaying yeast whole-cell biocatalyst could repeatedly catalyze the polyester, polybutylene adipate, synthesis reaction, using adipic acid and 1, 4-butandiol as the monomer molecules, four times in succession. This is the first report of the polymer synthesis using enzyme displaying yeast as the catalyst. The ratios of cyclic compounds in the polybutylene adipates synthesized with the CALB-displaying yeast whole-cells were lower than that in the polybutylene adipate synthesized with conventional metal catalysis. From these results, it appears that the use of CALB-displaying yeast cells could be useful for the polyester synthesis reaction, with reduced by-product production.