A bioinformatics method was used to analyze the characteristic dipeptides responsible for optimum temperature of xylanase in the F/10 family. It was found that the positive dipeptides are: TD, GH, and WY; and the negative dipeptides are: GA, IA, FH, LH, SR, and NH. The calculated temperature fitted the optimum temperature of the xylanase very well and the maximal and minimal optimum temperatures were calculated as. 150.46 and -29.06 degreesC. The thermostable mechanism was discussed and the result is useful for xylanase engineering for high temperature activity, for it also provided position information for engineering. (C) 2004 Elsevier Ltd. All rights reserved.