A fragile cell wall mutant strain of Saccharomyces cerevisiae was prepared by a single step disruption of the KNR4 gene, which is involved in cell wall biosynthesis. The enhanced transport property of the mutant cell across the loosen cell wall was confirmed by the increased drug permeability. The KNR4-disrupted mutant strain released the ectopically expressed foreign protein more easily than the wild type by mechanical disruption of the cell walls using glass beads, demonstrating a potential utility of using the mutant strain as a host for the efficient extraction of recombinant proteins.