Highly dispersed iron-based catalysts are being examined for the initial stage of direct coal liquefaction. Ultrafine (< 10-nm) particles are produced by a variety of methods. Mossbauer spectroscopy, magnetometry, XAFS, electron microscopy, XRD line broadening, and BET surface area measurement are used to estimate the particle size of the catalyst precursor and, in some instances, of the phases found consequent to the reaction process. With Mossbauer and magnetization techniques, data have to be obtained over a range of temperatures, usually from 4 to 300 K. In addition, obtaining the particle size by Mossbauer spectroscopy requires a knowledge of the magnetic anisotropy energy. Far some XRD lines, the broadening is a consequence of the presence of fault planes rather than crystallite size. An examination of the Fe-S phase diagram shows that the phases found at room temperature could be different from those that ace present under liquefaction conditions. The utility of the characterization techniques will be evaluated, and comparative results that are available will be presented. In situ characterization of catalysts under simulated liquefaction conditions is required.