A series of biodegradable poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) (PCL-PEG-PCL) (PCEC) triblock copolymers had been successfully synthesized by ring-opening polymerization of epsilon-caprolactone initiated by PEG, which were characterized by proton nuclear magnetic resonance analysis (H-1 NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The gel-sol phase transition diagram of synthesized copolymers was recorded using test tube inverting method. PCECs could form injectable solutions via self-assembly and automatically turned into non-flowing gels at physiological temperatures. Their aqueous solution displayed special gel-sol transition behavior with temperature increasing from 0 to 60 degrees C, when the polymer concentration was above corresponding critical gel concentration (CGC). In vitro release experiments at pH 7.4 showed that after 24 h at least approximately 75-80% of doxorubicin (DOX) can be protected from enzyme or hydrolytic degradation. Therefore, thermosensitive PCECs have many advantages, such as simple drug formulation, no organic solvent, a sustained drug release behavior.