The influence of different parameters such as particle size, initial weight of the sample, and heating rate on the devolatilization of wheat straw particles have been studied using thermogravimetric analysis. In addition, the variations in proximate analysis with different particle sizes of wheat straw have also been investigated. Results show that the curves corresponding to the third stage of pyrolysis differ for variations in particle size, initial weight, and heating rate of the pyrolysis process. A devolatilization model with three parallel nth-order reactions has been considered to determine the global kinetic parameters using thermogravimetric data. The kinetic parameters such as activation energy (kJ/mol), frequency factor (1/min), and order of the reaction for the three stages considered in devolatilization model were E-1 = 69, E-2 = 78, E-3 = 80; k(01) = 2.57 x 10(12), k(02) = 3.97 x 10(7), k(03) = 3.17 x 10(6); and n(1) = 2.3, n(2) = 0.65, n(3) = 2.7, respectively. It was noted from the order of the reaction that the second stage of the pyrolysis curve corresponds to the degradation of cellulose and hemicellulose, and the third stage to the lignin degradation. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.