Hemicellulose isolated from DmM was converted to novel functional biopolymers by maleylation using maleic anhydride as reactant and LiOH as catalyst. The reaction was performed under various temperatures, times, and the amounts of catalyst and maleic anhydride on the degree substitution (DS) of products were discussed. Comparison of the reaction in different media was discussed in detail. The product had the maximum degree of substitution (DS) of 0.75. Novel functional polymers containing with carbon-carbon double bond and carboxyl groups could be confirmed by 13C NMR spectroscopy. The behavior of novel hemicellulosic derivatives was monitored by means of thermogravimetry (TG) and differential thermal analysis (DTA). It was found that the products with a high DS had a lower thermal stability than the native hemicelluloses.