Experimental and theoretical investigation about coal/char structure is presented. Surface structures of parent coal and char with different burn-off ratios were analyzed. We introduced the fractal theory into Scanning Electron Microscopy image analysis and utilize the particle surface fractal dimension (D-ps) to quantitatively describe the surface character of coal/char particles. D-S of three Chinese coals reach their maximum in the 35-45 wt% char burn-off interval and then decrease with increasing carbon burn-off ratio. The inner-pore information of coal/char particles was determined by N-2 isotherm adsorption/desorption. Using fractal BET model, internal surface fractal dimension (D-S) of coal/char particles was calculated. The D-S change trend of three Chinese coals is similar to their SBEI development. It means the D-S can quantitatively describe the inner pore structure character of coal/char particles. (C) 2004 Elsevier Ltd. All rights reserved.