Proximate analyses, heating values and natural radionuclide contents (U-238, Th-232, K-40) of 36 samples of bituminous coals and 4 samples of anthracite were determined. The proximate analysis data and higher heating value were correlated by multiple linear regression analysis with the radionuclide contents. For each coal rank, the correlations obtained (giving in most cases r(2) > 0.9) an comparable with previous correlations based on measurements of natural gamma-ray activity of coal. Some improved correlations were obtained by considering separately the coals from each washing plant, with a degree of accuracy in accordance with the reproducibility tolerances of the Spanish and international standards UNE 32004, 32019 and ISO 1928-76.