Abstract: Biodegradation by Trichoderma pleuroticola T9 on lignite from Shanxi province was studied aiming to optimize the process in regard to the particle size and slurry concentration of the coal, as well as the inoculum quantity and fermentation time. The results indicated that the biodegradation was affected in the order of particle size inoculum quantity concentration of coal slurry duration of fermentation. The optimized conditions to achieve the maximum degrading rate of 60% were determined to be (a) a use of lignite with a particle size of 0.1 mm, (b) a coal slurry concentration of 2%, (c) the inoculation of 10 mL of T. pleuroticola T9 fermentation broth, and (d) incubation for 14 d.