Separation of bioproducts plays a key role in bio-industry. Aqueous two-phase systems are suitable for separation and purification of bioproducts like proteins, antibiotics, amino acids and organic acids. However, a key problem is the recovery difficulty of the copolymers forming aqueous two-phase systems. In the study, novel recyclable aqueous two-phase systems have been developed by using two new thermo-sensitive copolymers, P-NBAa and P-NDB. Copolymer P-NBAa was copolymerized by using N-isopropyl-acrylamide (NIPA), n-butyl methacrylate (BMA) and allyI alcohol (Aa) as monomers. Copolymer P-NDB was synthesized by using N-isopropylacrylamide (NIPA), 2-(dimethylamino) ethyl methacrylate (DMAEMA) and n-butyl methacrylate (BMA) as monomers. The lower critical solution temperatures (LCST) of these two polymers are 25.5 degrees C and 31.3 degrees C, respectively. P-NBAa and P-NDB can form aqueous two-phase systems with each other. Both of the two polymers can be recycled by adjusting temperature, with recoveries of over 97%. Demeclocycline was partitioned in the aqueous two-phase systems, with optimized partition coefficient of 2.61. It is believed that the recycling aqueous two-phase systems have potential applications in bioseparation engineering and biocatalysis engineering areas. (c) 2013 Elsevier B.V. All rights reserved.