An indigenous strain of Aspergillus niger AU15 which produced lipase constitutively was used to produce mutants using ultraviolet and N-methyl-N-nitro-N-nitosoguanidine. A mutant strain with lipase productivity of 2-fold higher was obtained. Optimization studies were also carried out. Dextrose as carbon source, peptone and cornsteep liquor as nitrogen source were found to be optimal for maximum lipase production.