A systematic analysis of the structure of char particles produced from an Illinois #6 coal was carried out. Coal particles were pyrolyzed in a hot-stage reactor under inert (N\sb2) and reactive (5% O\sb2 / 95% N\sb2) atmospheres at various heating rates (0.1, 1 and 10\sp∘C/s) and final heat treatment temperatures (500 and 700\sp∘C). Image analysis procedures were used to measure the size and macroporosity of the particles, and the surface area and size distribution of the macropores. High heating rates and the addition of oxygen resulted in larger particle swelling and increased the macroporosity, the surface area and the fraction of large macropores with thin walls. Heat treatment temperatures had smaller effects on char particle structure. Our data confirm the strong effects of pyrolysis conditions on char reactivity during combustion in the diffusion-limited regime. They also provide the necessary parameters for char combustion models.