The kinetics of lignin (ammonium-based lignosulfonate and sodium-based lignosulfonate) methylolation were studied in solution by monitoring the rate of disappearance of form-aldehyde and by using differential scanning calorimetry (DSC) techniques under an iso-thermal program, at 20, 40, 50, and 60°C, respectively. The kinetic parameters obtained from these two methods agree with each other. The results show that the degree of lignin methylolation depends on the number and availability of reactive sites per C9 unit of lignin. Lignin methylolation has a lower activation energy and a lower preexponential factor than that of phenol methylolation. Lignins took a shorter time to reach complete methylolation than did phenol at the low temperatures used here. © 1993 John Wiley & Sons, Inc.