Raman spectroscopy is potentially a very useful technique for characterizing heterogeneous carbons and cokes. This paper describes an investigation of the relationships between Raman spectral parameters, optical reflectance measurements, and crystallite diameter, L a , determined by X-ray diffraction measurements. It is shown that the Raman D (1360 cm −1) bandwidth correlates with L a for cokes with heat treatment temperatures in the range 500–1900 °C, the bandwidth decreasing as the crystallite diameter increases. The X-ray diffraction and Raman measurements do not correlate with the reflectance measurements. These results are discussed in terms of the coke structure and they suggest that Raman spectroscopy and reflectance measurements are potentially useful for characterising differences in thermal history in heterogeneous char samples.