[Objective] Exploring a purification method of uricase modified by polyethylene glycol to improve the efficiency of separation and purification, retain the activity of the enzyme, wide applicability, easy to expand production [Method] The 60% saturated ammonium sulfate solution was preliminarily purified, anion column chromatog., and finally purified by mol. exclusion method. [Result] After purification, the purity of uricase was 100%. NHS and PEG residues were purified and separated, and each uricase monomer was stably modified by 10 peg. [Conclusion] After optimization, the NHS and unresponsive urase were removed by anion chromatog. PEG modified urate was captured by gel filtration chromatog. The purity of pegylated uricase protein was 100% by reverse phase purity test and polymer purity test. The detection data of PEG residue and NHS residue were zero.