The thermoresponsive transition behavior of a diblock copolymer consisting of poly(ethylene glycol) methyl ether (mPEG) and poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) in aqueous solutions has been investigated. With a specific composition, the copolymer showed a unique tunable phase transition from no response in acidic media to a solubleinsoluble (S-I) transition in neutral media and an S-I-S transition in basic media either in the presence of salt or for salt-free solutions. The S-I-S transition can be tuned over a wide temperature range even to an S-I type transition just by adding salts. In addition, phase transitions can occur in both pure water and saline solution under practical conditions (3080 degrees C), which makes them suitable for a broad range of applications.