Inulin was carboxymethylated in aqueous alkaline medium with monochloroacetic acid as the reagent. The degree of substitution of the reaction product was determined by titration, LC analysis and 13C NMR spectroscopy. Carboxymethylinulin with a degree of substitution between 0.2 and 1 was obtained depending on the molar ratio of inulin-monochloroacetic acid. Increasing the concentration of the reaction mixture and lowering the reaction temperature resulted in higher selectivities towards carboxymethylinulin. Determination of the molecular weight distribution was performed by GPC and by multi-angle laser light scattering. Carboxymethylation caused little or no degradation of the chain length of the starting material.