Octenyl‐succinic anhydride (OSA)‐modified starch was used as an emulsifier in oil‐in‐water emulsions. Multiple analytical techniques, including size‐exclusion chromatography (SEC), confocal laser scanning microscopy (CLSM), and laser diffraction particle size analysis were used to determine the structure and emulsification properties of OSA‐starch. The results indicated that OSA‐starch with a smaller molar mass exhibited improved emulsification properties than its larger counterparts. Furthermore, samples pretreated by enzymatic modification for 25 min showed the best droplet size distribution, improved emulsion stability, and minimum aggregation. It was also determined that stable emulsions were not formed when the average molar mass of OSA‐starch was too small. The emulsion ability of OSA‐starch enzymatically modified for 35 min was found to be a little inferior than that of OSA‐starch upon enzyme treatment for 25 min.