Magnetic properties of coal samples were studied by using electron spin resonance (ESR) spectrometer. The spectra linewidth were determined from ESR measurement results. We observed that these parameters depend on heating temperature. Spectra of all samples showed both broadening and narrowing phenomena. It is indicated that the change of spectra linewidth is due to dipolar interactions of unpaired electrons and the unresolved hyperfine structure of interactions of unpaired electrons with neighbouring protons.