Gasification kinetics of wheat straw char with CO2 was investigated using Thermogravimetric apparatus (TGA). The main objective was to identify the diffusional and surface reaction phenomena that may occur during biomass char gasification experiments with CO2. The effects of temperature (750-900 degrees C) and particle size (< 60-925 mu m) on gasification rate of char-CO2 reaction were determined. The 50% conversion (r(50)) rate showed that the reactivity increases with temperature, and it decreases as the particle size increases. The important diffusional parameters such as effective diffusivity, effectiveness factor and Thiele modules were calculated based on the experimental data and the results showed that the impact of physical factors is prominent at high temperature and large particle sizes. It was found that char gasification within the temperature range studied followed the chemically controlled reaction regime and the influence of pore diffusion was negligible for the fine powder particles. (C) 2010 Elsevier Ltd. All rights reserved.