The usefulness of Taguchi method for optimization of culture condition, designed for production of xylanase by Trichoderma longibrachiatum was investigated. L16 orthogonal array, by which the effect of five factors in four levels, could be tested, was chosen. Analysis of variance (ANOVA) was performed on the obtained results and optimum condition suggested by statistical calculations was tested in a verification test. An increase of 41.9% in xylanase production was observed, after performing optimization techniques, including one-factor-at-a-time (OFAT) and Taguchi method, which indicates suitability of this method in microbiological processes optimizations.