Abstract: The effects of the initial pH value on xylanase and cellulase synthesis by Trichoderma reesei Rut C 30 have been investigated.The results show that low initial pH value could stimulate the synthesis of cellulase,whereas the high initial pH value could prolong culture time of xylanase synthesis and depress the synthesis of cellulase,therefore the high initial pH value could favourate the synthesis of cellulase poor xylanase.When the initial pH values were 4.0,4.4,4.8,5.4,6.0,the ratio of xylanase to cellulase was 259,327,425,865,1 016,respectively,after 72 h cultivation.The ability of consumption of reduce sugar in the culture filtrate decreased by Trichoderma reesei with increasing of the initial pH value,When the initial pH value was 4.0～4.8,the concentration of reduce sugar in the culture filtrate maintained a low level,and reached the lowest concentration in 48 h;When the initial pH value was 5.4～6.0,the concentration of reduce sugar in the culture filtrate was high,and reached the lowest concentration in 72 h;When the initial pH value was 6.5,the concentration of reduce sugar in the culture filtrate was higher,and the synthesis of xylanase and cellulase was depressed.