p-Toluenesulfonyl-lignin was prepared by reacting lignin with p-toluenesulfonyl chloride (TsCl) in an aqueous medium. The reaction was performed at 25 degrees C. The influence of several parameters on the reaction efficiency has been studied, including the ratio of p-toluenesulfonyl chloride/hydroxyl of lignin (TsCl/OH), the amount of triethylamine (Et3N), and the reaction time. The resulting p-toluenesulfonyl-lignin samples were characterized by means of scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX), attenuated total reflection (ATR), and the X-ray photoelectron spectroscopy (XPS). Detailed structural characterization of the products, including elemental analysis, indicates that the synthetic approach leads to products without impurities. The tosylation reaction is complete after 24 h.