The production of inulinase in Kluyveromyces sp. Y-85 is repressed by the carbon catabolites. To screen for derepression mutants, the strain of Kluyveromyces sp. Y-85 was treated with the mutagenic agent, ethyl methane sulfonate (EMS). Initially, mutants resistant to catabolite repression by 2-deoxy-D-glucose were isolated. One such mutant, Kluyveromyces sp. Y-85 Kg, was found to exhibit stable, 2-fold higher expression of inulinase than the wild-type in glucose-containing medium, indicating that it is a promising strain for industrial production.