Abstract: In order to study optimum conditions for dodecenly succinic anhydride-modified inulin,effects of the amount of inulin,the dosage of sodium borohydride and dodecenly succinic anhydride (DDSA),pH,time and temperature used on the degree of substitution of dodecenly succinic anhydride - modified inulin were investigated. Plackett -Burman was adopted to screen out the important factors,which were the dosage of dodecenly succinic anhydride,pH and time used. The optimum reaction conditions were obtained by response surface analysis:inulin 4g,sodium borohydride 0.015g,dodecenly succinic anhydride 0.94g,time 6.8h,pH8.5, temperature 35℃ ,and the degree of substitution of dodecenly succinic anhydride-modified inulin is 0.0140 ± 3.33E-05.