A mutant Candida sp 99-125 with high lipase activity was screened by a series of mutation methods including UV light, N-methyl-N-nitro-N-nitroso-guanidine (NTG) treatment and quick neutron mutation. The lipase produced increased ten times compared with the parent. The fermentation medium including nitrogen sources, carbon sources and metal ions for lipase production from Candida sp. 99-125 was optimized and the optimal medium composition consisted of 4% soybean meal, 2.5% (w/v) soy bean oil, 0.1% (w/v) K2HPO4, 0.1% (w/v) (NH4)(2)SO4, 0.05% (W/V) MgSO4, pH 7.0. The fermentation conditions were also studied and incubation was carried out at 28 degreesC with an agitation rate 500 rpm and an aeration rate 1:1 vvm in a 30 1 fermenter. The scale up of the fermentation was made from 30 1 fermenter to 1500 1 fermenter and the results indicated that Candida sp 99-125 is a stable and high lipase producing mutant strain. The lipase activity produced in a large fermenter (1500 1) reached 8060 U/ml. (C) 2003 Elsevier Science Ltd. All rights reserved.