The effect of Ni-, Co- and Fe-substitution for Cu on the thermal conductivity of La5Ca9Cu24O41 thin films is investigated. Highly 6-axis oriented polycrystalline films were grown onto MgO (100) substrates using the pulsed laser deposition technique. Thermal conductivity measurements were made between 90 K and 300 K using the dynamic 3 omega method. The room-temperature thermal conductivity of 1% Ni:La5Ca9Cu24O41 and 1% Co:La5Ca9Cu24O41 is approximately 15% smaller than the thermal conductivity of pristine La5Ca9Cu24O41 thin films of similar thickness. On the other hand, the thermal conductivity of 1% Fe:La5Ca9Cu24O41 is approximately the same as the thermal conductivity of pristine La5Ca9Cu24O41 thin films of similar thickness. These results enable us to indirectly conclude that Ni2+ and Co2+ ions substitute Cu2+ ions in the crystal structure while Fe ions are not incorporated in the lattice. (C) 2009 Elsevier B.V. All rights reserved.