Mutants of the strain producing natamycin, Streptomyces gilvosporeus, were obtained after space-flight mutation. With respect to the sand spores and slant spores, the mutation ratios were up to 67.6% and 78.3% and the survival ratio was 43.1% and 3.0%, respectively. An improved mutant producing natamycin, S. gilvosporeus LK-45, was screened, which showed natamycin productivity of 1420mg center dot L-1. A mutant resistant to 2-deoxy glucose, S. gilvosporeus LK-119, was further obtained using a rational screening procedure. The natamycin productivity of 1940 mg-L-1 was achieved when glucose was used as the carbon source.