In order to improve the operational performance of the oxalate decarboxylase( Oxdc) which can be used to prevent and treat calcium oxalate stone,modification of Oxdc by methoxy polyethyleneglycol was studied, some enzymatic properties of wild enzyme( Oxdc) and modification enzyme( mPEG-Oxdc) had been determined. The modification conditions were preliminary optimized according to the single-factor experiment,and the optimal results were as follows: under a weak acid environment( pH5. 0),a mole ratio of mPEG-aldehyde/Oxdc for 50∶ 1,the modification was occurred at 37℃ for 12 h,which could remain about 67. 52% of enzymatic activity and the modification rate was 50. 69%. SDS-PAGE and FT-IR analysis turned out that the mPEG had covalently bound to the enzymatic protein. Furthermore,analysis of enzymatic properties found that the Oxdc lost almost total of enzyme activity,but the mPEG-Oxdc maintained 21. 6% after heating treatment. The activity of mPEG-Oxdc was always higher than the Oxdc during pH2. 0 ~ pH6. 0. As the activity of Oxdc went down to 20. 6%,the mPEG-Oxdc kept 47. 1% after trypsin treatment. All the results demonstrated that the thermostability,resistance to acid,heat and trypsin of mPEG-Oxdc had been improved relatively.