The fraction of the stacking structure (PS) and the average number of aromatic layers (Nave) in several raw coals were estimated by X-ray diffraction analysis (Standard Analysis of Coal by XRD: STAC-XRD). STAC-XRD is more appropriate for analyzing coal with low crystallinity than the classical XRD analysis method by using the interlayer spacing of aromatic layers (d(002)) and the mean crystallite size along the c axis (L(c)). STAC-XRD was also used to compare the development of the stacking structure in caking coal during heat treatment with that in non-caking coal. After heat treatment at 920 degreesC, N(ave) of the caking coals was larger than that of the non-caking coals. The stacking of the aromatic layers in the caking coal temporarily developed at the fluidity stage at 400-440 degreesC, but in the 440-600 degreesC range, the release of volatile components partially disordered the stacked layers. The influence of heat-treatment conditions on carbon stacking structure in several kinds of coal was investigated by means of STAC-XRD. The heating rate required for the development of stacking structure in lower-rank coals was slower than that required for higher-rank coals. (C) 2004 Elsevier Ltd. All rights reserved.