Abstract: AIM　To study the effect of thermal denaturation on the water-solubility and enzymatic degradation of spray-dried bovine serum albumin (BSA) microspheres (MS), and to investigate the mechanism of thermal denaturatiom. METHODS　Microspheres were prepared by spray-drying of BSA solution, and further stabilization of the spray-dried powder in a hot air oven at 120℃ for 3, 6, 12 and 24 h or for 6 h at 100, 120, 140 and 160℃,respectively. UV analysis was used to determine the percentage of the BSA dissolved in water. Microsphere degradation in trypsin medium was studied by naked eyes and optically microscopic examination. Fourier-transform infrared spectroscopy was used to study the secondary structure of the spray-dried albumin microspheres. RESULTS　BSA-MS water-solubility was significantly decreased, and the time for enzymatic total degradation increased, as the heating time prolonged and temperature elevated. These demonstrate the influence of heating time and temperature on microsphere degradation. CONCLUSION　The functions of thermal denaturation may have something to do with the changes of secondary structure of albumin. Thermal denaturation may affect the α-helix and β-sheet structure content of the microspheres. Water-solubility and enzymatic degradation of BSA-MS can be controlled through choosing appropriate thermal denaturation conditions, which suggests that the release rate of spray-dried drug-loaded BSA-MS, as a controlled drug delivery system, can thus be controlled to a desired extent.