The polymer with appropriate hydrophilicity is critical to the design and preparation of a drug release system.We employed poly-(monomethoxypolyethylene glycol-co-D,L-lactide) (mPEG-PLA,PELA) with different hydrophilicities based on various ratios of mPEG to PLA to prepare microspheres.Contact angle, atomic force microscope (AFM), and quartz crystal microbalance with dissipation (QCM-D) techniques were first combined to elucidate the microcosmic mechanism of incomplete release.In addition, the pH change within the microsphere microenvironment was monitored by confocal laser scanning microscopy (CLSM) employing a pH-sensitive dye, which clarified the stability of rhGH during the release.These results suggested that polymer hydrophilicity played an important role in rhGH incomplete release and stability.