The thermostablility and enzymatic activity of 1,3-1,4-beta-glucanase (BglA) from Bacillus amyloliquefaciens was improved by modifying five (out of 12) epsilon-amino groups in lysine residues with nitrous acid. The optimal modification condition for BglA was determined as 30 mM nitrous acid at, 40 A degrees C for 30 min. The optimally-modified BglA had higher specific activity and T (50) value, which were 3,370 U/mg and 70 A degrees C, respectively. Its half-life values at 50 and 60 A degrees C were extended and reached 58.5 and 49.5 min, respectively. Circular dichroism analysis showed that the secondary structures in modified BglA were almost the same with that of wild-type BglA. Thus, modification of lysine residues can simultaneously improve the activity and thermostability of beta-glucanase which are ideal targets for further protein engineering.