Granular and crystalline structures of resistant octenyl succinic anhydride (OSA) modified corn starch were characterized using scanning electron microscopy (SEM), optical microscopy and X-ray diffraction. As a colon-targeted delivery carrier, the releasing property of resistant OSA-modified starch was also investigated by In-vitro model. Enhanced succinylation of starch considerably increased the enzyme and acid resistibility to digestion, indicating the improvement of starch colon-targeting property as the degree of substitution (DS) increased. From In-vitro releasing assay, the resistant OSA-modified corn starch based matrix tablets could deliver bioactive components to the colon when the RS content and hydrophobicity were suitable. The relationship between the structure and In-vitro release properties of resistant OSA-modified corn starch suggests that an optimal DS and crystalline:amorphous ratio can be responsible for 5-ASA release. The matrix tablets used resistant OSA-modified corn starch with moderate DS (0.60) and V-type crystal morphology co-exist with the amorphous structure as carrier show good colon-targeted releasing properties.