A novel process was developed for the butyration of lignosulfonate (LS) with butyric anhydride in the presence of choline chloride at elevated temperatures. The degree of substitution (DS) was qualitatively and quantitatively determined by Fourier transform infrared spectroscopy using the baseline method. It was found that the DS of butyrated LS products increased from 0 to the range of 0.41 to 2.14 with the addition of choline chloride, indicating that butyric anhydride-choline chloride is a novel and highly effective solvent for the butyration of LS. The DS of butyrated LS was dependent on choline chloride dosage, reaction temperature, reaction time, and the mass ratio of butyric anhydride to LS. Characterization results by proton nuclear magnetic resonance spectroscopy further demonstrated the occurrence of the butyration reaction. The results of thermogravimetric analysis showed that the thermal stability of the butyrated LS decreased with increasing degree of substitution.