The di-peptides positively correlated with optimal temperature in G/11 xylanase are computed to be: LA, LG, CR GD, RY, CH; the negatively ones are: DC, Y1, YP, and CR The comparison of the structures of rnesophilic and thermophilic xylanase showed that these dipeptides predominantly occur in beta-turns. These results explain the successful improvement of thermostability by introducing arginines into the xylanase surface area and therefore have implications for xylanase engineering (c) 2005 Elsevier Ltd. All rights reserved.