The structural evolution of rice husk char particles during steam gasification was studied by ultimate analysis, inductively coupled plasma atomic emission spectroscopy, scanning electronic microscope, N-2 physisorption method and X-ray diffraction. Drastic changes in char structure occurred even when the char conversion was minimal. The C, H and O content decreased by more than 85%. 67% and 91%, respectively. The H/C atomic ratio always increased, while the O/C exhibited a "similar to" shape. The maximum porosity appeared at char conversion of 48.6%. D-s and d(ave), showed a good linear relationship. Aliphatic structures and smaller aromatic rings tended to be preferentially consumed to left the char more ordered and enriched with larger aromatic ring systems. The presence of steam favored the volatilization of Na. K, Mg and Ca showed a similar behavior and their concentrations reached maxima at 60.3%. Great loss of O-containing structures caused significant volatilization of K, Mg and Ca. (C) 2012 Elsevier Ltd. All rights reserved.