This paper reports an experimental study to assess the effects of CO2 and heating rate on the characteristics of the chars formed in CO2 and N-2 atmospheres in the initial stage of oxy-fuel combustion. The chars of a Chinese bituminous coal were prepared in a fluidised-bed/fixed-bed reactor at 900 degrees C and their chemical structural features were further characterised with FT-Raman spectroscopy. Our results indicate that changes in CO2 concentration influence not only the char yield but also the char chemical structural features, which become more condensed and increasingly oxygenated with increasing CO2 concentration. The chars formed in CO2 atmosphere at fast heating rates are less condensed but more oxygenated than those formed at a slow heating rate. The O-holding capacity of the fast heating char decreases with the aromatic condensation as the char is held in CO2 atmosphere at 900 degrees C. (C) 2014 Elsevier Ltd. All rights reserved.