Preparation of esterified starch with low substitution degree was studied by using potato starch as raw material, succinic acid anhydride as esterifying reagent, water as solvent, substitution degree as evaluating index. The viscosity and transparency of product were determined and analyzed. Results : The proper reaction conditions are reaction time 60 min, reaction temperature 30 ℃, pH 9.0, succinic acid anhydride dose 4%. The product transpar-ency and viscosity trend increase with substitution degree rising. The transparency and viscosity of the esterified pota-to starch are better than raw potato starch and esterified corn starch.