Although coal blends are increasingly utilized at power plants, ash slagging propensity is a non-additive property of the pure coals and hence difficult to predict. Coal ash tendency to slag is related to its bulk chemistry and ash fusion temperatures, and the present study aims to compare the results obtained from thermodynamic simulation with characterization of samples obtained as outcomes of plant-based coal-blend combustion trials at three utilities located in the Centre and North of Chile. Pulverized coal and plant residues samples from five families of binary blends tested in an experimental program were characterized for chemistry, mineralogy and maceral composition. The slagging was evaluated by determination of fusion curves using the MTDATA software and NPLOX3 database for the main coal ash oxides. The ranking obtained was approximately the same as obtained from carbon in the fly ashes and from plant residues observations. The thermodynamic modeling was a valid option to predict the fusibility during the combustion of blends. (C) 2003 Elsevier Ltd. All rights reserved.