Affinity precipitation is considered as a promising technology for the purification of proteins at an early stage of downstream processing.The technology applies reversible soluble-insoluble polymers coupled with ligands as an affinity carrier to purify proteins from large volume of dilute solution material and archives recycle of affinity polymers.Cellulase, enzyme complex composed of hydrolytic and oxidative enzymes, can catalyze the degradation of cellulose to glucose.It comprises endo-glucanase (endo-1,4-β-D-glucanase, EG), exo-glucanse (exo-1,4-β-D-glucanase, CBH) and cellobiase (β-1,4-glucosidase, BG).It is well known that cellulase will play a key role in future bioenergy and biochemicals industry.Currently, cellulase is only applied by in a form of crude enzymes and could not be recycled efficiently.It is indispensable to obtain pure cellulase and to recycle it at a very low cost in bioindustry.In this study, cellulase was purified by using affinity precipitation with pH-response polymer coupled with dye ligand to obtain electrophoretically pure cellulase.A commercial crude cellulase (Novozymes) from Trichoderma reesei was used as experimental material.A pH-response copolymer PMMDN was synthesized in our group.Here, CB was coupled to the polymer via the nucleophilic reaction between the active chlorine atom of its triazine ring and the hydroxyl group of the polymer.The isoelectric point of the affinity polymer was 5.0 and the recovery was 99.8% in presence of 0.8 mol/l Na2SO4.The adsorption and elution of cellulase on the polymer was investigated and the reusability of the polymer was also studied.Optimal adsorptions could be achieved at pH7.2 and 1.0 mol/1 NaCl.0.1 mol/l Tris-HC1 (pH 7.1) with 20.0% glycol was used as eluant and the elution recovery of total cellulase activity and endo-glucanase activity was almost 84.4% and 99.8%, respectively.The SDS-PAGE showed the main bands with a molecular weight corresponding to that of the native cellulase.