A mutant of Candida tropicalis FYD-2 was obtained from its parental strain SFP-1186 by ultraviolet treatments. On shaking flask, the yield of mixed dicarboxylic acid(DCA) by the mutant was 21.4% higher than that by its ancestor. The amount of mixed DCA reached 156 g/L for 120 h incubation in a 10 L autoconrolled fermentor where the culture medium contained 25% n-paraffin. The process of induced and screening mutant was introduced and the time course of fermentation in 10 L fermentor was discussed.