This work primarily focusses on understanding the interaction of lignosulfonate (LS) and oxidized sulfomethylated lignin (OSL) with coal particles in a coal water slurry (CWS). LS had a charge density of -1.8 meq/g and sulfonate group content of 1.6 mmol/g, while OSL had a charge density of -1.8 meq/g and sulfonate group content of 0.6 mmol/g. LS adsorbed more on coal particles than did OSL (0.26 mg/g), and the adsorption of LS decreased with increasing the coal particle size. LS improved the wettability of coal by reducing the interfacial tension between coal particles and water. Coal particle's size significantly affected the adsorption of LS on coal surface and hence the rheological behaviour of CWS. The rheological studies confirmed that IS improved the stability of coal particles more than OSL via introducing repulsion force between the particles in the suspension. (C) 2019 Elsevier B.V. All rights reserved.