In this study, a novel pH-sensitive terpolymer PADB was synthesized by random terpolymerization of 2-(dimethylamino) ethyl methacrylate, acrylic acid, and butyl methacrylate. The terpolymer PADB could form aqueous two-phase systems (ATPS) with a light-sensitive terpolymer PNBC, which was synthesized in our laboratory, using n-isopropylacrylamide, n-butyl acrylate, chlorophyllin sodium copper salt as monomers. More than 97% of the PADB terpolymer could be recovered by adjusting the pH to isoelectric point (PI) 4.1. The terpolymer PNBC could be recovered by using light radiation at 488 nm, with recovery ratio of 98%. BSA and lysozyme were partitioned in the PNBC-PADB ATPS to examine this new system. It was found that the partition coefficient of BSA and lysozyme could I-each 4.46 and 0.49 in the systems, respectively. (C) 2009 American Institute of Chemical Engineers Biotechnol. Prog., 25: 820-824, 2009