Mercury(II) complexes of some pyrimidine derivatives were prepared and characterized by elemental analysis and spectral measurements. The1H n.m.r and i.r. spectra show the ligands to be in the keto form. Thermal analysis and electrical conductivity measurements of the complexes were investigated in the temperature range 30–250°C. The results indicate slight semiconducting behaviour. The disparity in the activation energy values, ΔE as calculated from the slopes of the linear parts of the electrical conductivity curves is due to the difference in the concentration of the imperfections contained in the different types of the complexes.