Magnetic susceptibility can be used for assessing anthropogenic pollution in solid matrices, including soils and composts. This work studies the distribution of trace elements and magnetic susceptibility in the different size fractions of six composts, for the development of measures aimed at reducing compost pollution at the production stage. The results showed that magnetic susceptibility decreased with increasing particle size in all composts, and the same was true for most trace element concentrations. Magnetic susceptibility was significantly correlated with Fe, as well as with Cu, Zn, Pb, Cr and Ni, which proves the relationship between the presence of ferric particles and trace element contamination in compost. Our results suggest that the association of trace elements and magnetic susceptibility is a characteristic feature in municipal solid waste composts.