The reactivity of octenyl succinic anhydride (OSA) with starch by phase transition catalyst (PTC) was investigated. The effects of two types (quaternary ammonium salt and non-ionic surfactant) and concentrations of PTC on the degree of substitution (DS) and reaction efficiency (RE) of OS-starch were examined. In aqueous medium, the use of a PTC, polyoxyethylene lauryl ether (AEO) produced derivatives with higher DS than others. The DS of OS-starch reached 0.0195 with 0.1% AEO, significantly higher than that (0.0182) without the use of PTC. As the concentration of AEO increased, the DS of OS-starch did not increase. The structural of AEO was investigated by nuclear magnetic resonance (NMR) spectroscopy. Conductivity measurement and Fourier transform infrared (FT-IR) spectroscopy confirmed that AEO could form complexes with Na + . The complex of AEO and Na + could combine with starch-O − , it should be possible to improve the transport of anion starch-O − to the hydrophobic reagents.