Some complexes of Pb(II) of thiosemicarbazone derivatives have been prepared. Structural investigations of the complexes have been made based on elemental analysis, spectral (UV–Vis, IR) studies and conductivity measurements. The thermogravimetry (TG), derivative thermogravimetry (DTG) and differential thermal analysis (DTA) have been used to study the thermal decomposition of the complexes. The photolyses of the free ligands and their Pb(II) complexes have been investigated. It was found that the photochemical behaviour of the Pb(II) complexes is similar to that of their corresponding free ligands. The photolysis is enhanced by the presence of H₂O₂ due to the hydroxyl radicals generated during the irradiation.  Also the photochemical reactions were faster in the presence of halocarbon solvents. Mechanisms of the observed photochemical behaviour have been suggested.