The aim of this study was to investigate the effects of particle size on the non-isothermal slow pyrolysis of hazelnut shell from ambient to 1173 K with a linear heating rate of 20 K/min under dynamic nitrogen atmosphere. For this purpose, the hazelnut shell with different particle size fractions in the range between -0.150 and +1.400 mm were used in the pyrolysis experiments that performed in a thermogravimetric analyzer (TGA). Some constituents of this biomass sample such as hemicellulose, cellulose, lignin and extractives were determined using analytical methods. Surface area measurements of the particle size fractions were performed using a BET analyzer. The microstructural characterization of the pyrolysis char was carried out using a scanning electron microscope with energy dispersive (SEM-EDS) attachment. It was found out that in case of larger particle sizes, high yields of char could be obtained, however higher apparent activation energy was needed for the pyrolysis process. (C) 2005 Elsevier B.V. All rights reserved.