In this article, biodegradable and low molecular weight poly(ethylene glycol)-poly(epsilon-caprolactone)-poly(ethylene glycol) (PEG-PCL-PEG, PECE) triblock copolymers were successfully synthesized. Aqueous solution of the obtained PECE copolymers underwent sol-gel-sol transition as temperature increased which was flowing sol at room temperature and then turned into nonflowing gel at body temperature. Sol-gel-sol phase transition behaviors of aqueous PECE solutions were studied using rheometry and test tube-inverting method, which were affected by many factors, including the heating/cooling procedure and different additives in copolymers aqueous solution. In vitro drug release behavior was studied using bovine serum albumin (BSA) and Vitamin B(12) (VB(12)) as model drugs, and the PECE hydrogel could protect BSA from acidic degradation for 1 week at least. Therefore, PECE hydrogel is believed to be promising for injectable in situ gel-forming controlled drug delivery system due to their great thermosensitivity and biodegradability.