The reaction of wheat straw hemicelluloses with succinic anhydride in aqueous alkaline systems was studied. The products showed a rather low degree of substitution, ranging from 0.017 to 0.21. The effects of reaction times of 0.5-16 h, temperatures of 25-45 degreesC, and molar ratios of succinic anhydride to anhydroxylose units in hemicelluloses of 1:5-1:1 on the succinoylation yield and degree of substitution were examined. With the reaction kept within a pH range of 8.5-9.0, a temperature range of 25-28 degreesC, a reaction duration of 1-2 h, and a 1:1 molar ratio of succinic anhydride to hemicelluloses were preferred. The structure of the resulting polymers was determined with Fourier transform infrared and H-1- and C-13-NMR spectroscopy, which indicated monoester substitution. The thermal stability of the esterified polymer increased with chemical modification.