The octenyl succinate starch is a stabilization-modified starch produced by esterification of native starch with octenyl succinic anhydride (OSA). When modified in this way the starch tends to improve its functional characteristics, can be used to tailor starch to specific food applications. Therefore, optimization of reaction conditions of octenyl succinate starch is critical for modification. The preparation of OSA starches from potato starch in an aqueous alkaline solution was investigated. The reaction conditions, including reaction temperature, OSA concentration, concentration of starch slurry, reaction time and pH, were studied and optimized, as they influence esterification. Under the optimization conditions, the degree of substitution (DS) could reach 0.01862. The products were confirmed by the presence of the carbonxylate signal around 1558 cm-1 in the fourier transform infrared (FT-IR) spectra. By scanning electron microscope (SEM), OSA starch granules were proved to transfer to some smaller anomalistic ellipses and had slight rough on their surfaces. X-ray diffraction showed that esterification occurred primarily in the amorphous regions and the crystalline pattern of starches did not change. The thermal characteristics of the OSA starch were studied by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA revealed that the OSA starch were thermally more stable than the native starch. The OSA starch exhibited 50 % weight loss at 320°C, while the native starch underwent 50 % weight loss at 312°C. The DSC results showed that amorphous region increased after esterification.