The thermal conductivity of various grades of pearlitic cast iron has been modelled with good results by means of regression analysis. The experimental thermal conductivity data, which the modelling is based on, were obtained by the laser flash method. The microstructure was investigated by digital image analysis combined with a colour etching technique. The model developed takes the carbon content, the silicon content, the nodularity as well as the fraction of cementite into consideration. The graphite morphologies of the samples investigated were lamellar, compacted and spheroidal.