In this article, we studied the effect of hyaluronic acid (HA) on thermogelation of poly(caprolactone-b-ethylene glycol-b-caprolactone) (PCL-PEG-PCL) aqueous solution designed as an injectable system for prevention of postsurgical tissue adhesion. The PCL-PEG-PCL triblock copolymers were simply synthesized by ring-opening polymerization of E-caprolactone (CL) in the presence of PEG as a polymeric initiator. The synthesized copolymers were confirmed by proton nuclear magnetic resonance (H-1-NMR) spectroscopy. Possible interactions between HA and PCL-PEG-PCL triblock copolymers in the blend were evaluated by Fourier-transform infrared spectroscopy (FTIR). The effect of HA on the micellization of PCL-PEG-PCL aqueous solution was investigated by dye solubilization method and electrophoretic lighting scattering (ELS) spectrophotometer. Also, the thermogelling behaviors of the PCL-PEG-PCL triblock copolymers in the presence of HA and their mechanism were investigated by test tube inverting method, C-13-NMR, H-1-NMR, Advanced Rheometic Expansion System (ARES), and differential scanning calorimetry (DSC). The PCL-PEG-PCL/HA blend aqueous solutions undergo the sol-gel-sol transition in response to an increase in temperature (10-60 degrees C) and the gelation of the PCL-PEG-PCL was rather accelerated by HA. Presumably, this accelerated gelation seems to arise from the attractive interactions between them and the effect of chain confinement in the micelle corona region. (C) 2008 Wiley Periodicals, Inc.