The synthetic conditions of octenyl succinic anhydrid( OSA) modified white dextrin ester and its emulsifying properties were investigated. The results showed that white dextrin was prepared by adding 0. 25% hydrochloric acid into cassava starch and drying at 105 ℃ before degradation at 130 ℃ for 2 hours. OSA white dextrin ester,with degree of substitution( DS) 0. 0517,could be formed under the following conditions: 14. 5% OSA,temperature 45 ℃,pH 8. 5,5 hours reaction. Infrared data showed that aliphatic absorption peak appeared at 1 640 cm- 1and 3 010 cm- 1,and carbonyl absorption peak appeared at 1 724 cm- 1. This demonstrated the formation of OSA was modified by white dextrin ester. Reaction time was controlled for 1 hour and 3 hours,two OSA white dextrin esters with DS 0. 0105 and 0. 0324 were obtained. The results also indicated that OSA modified white dextrin esters were soluble in cold water and the emulsion stability were increased with DS values,this was due to the increase number of hydrophobic groups on white dextrin molecules. After one month storage,D50of the emulsion solution did not changed much.