Reactive aqueous two phase system (ATPS) using hydrophilic polymer and dextran was applied to recover the cellulase. Copolymer consists of polyethylene oxide (PEO) and maleic acid anhydride (MA) was used to modify the cellulase. By controlling the ratio of ethylene oxide, hydrophilic property of copolymer was controlled, and the MA functional group of copolymer covalently coupled with the amino groups of cellulase. The two phase system was mixed with dextran and copolymers with molecular weight of 505,000. The modified cellulase with reactive copolymer moved to the upper phase, PAG copolymer phase while the impurity moved to the down phase, dextran phase. As a result, most enzymes, approximately over 70 %, moved to copolymer phase. Therefore, reactive aqueous two phase partition by modification of cellulase is very effective to separate enzyme from the fermentation broth.