The conidia of Pseudomonas Migula Y 1were mutagenized by NTG, Co 60 and UV respectively. Chitosanase-producing mutant of Pseudomonas Migula Y 8 was obtained by screening with the method of transparent zones . Its chitosanase activity was 3.0 U?mL, -1 which has increased by six times approximately. The method of UV was better than others.