A strain of Aspergillus niger (G-IV-10) most effective for simultaneous production of catalase and glucose oxidase (GOD) was selected out of molds belonging to 15 different species by the method of test-tube microculture. Conidia of the selected strain were further subjected to mutagenesis with both UV and N-methyl-N’-nitro-N-nitrosoguanidine (NTG) and the products were analyzed for catalase activity with our own diffusion plate method. Among 1,055 strains isolated after mutagenesis Eight showed higher catalase (from 44-102.1%) and GOD (from 8.9 to over 77%) activities than the starting Aspergillus niger G-IV-10.