Microstructure and thermoelectric properties were investigated on Zn4Sb3 thin films prepared by co-deposition of Zn and Sb by magnetron sputtering. The as-deposited amorphous thin films were annealed at temperatures between 573 and 673 K so that they crystallized in the form of beta-Zn4Sb3. The Zn4Sb3 thin films have a relatively high power factor and a low thermal conductivity Microstructure of the thin films can be controlled by changing sputtering power and deposition time. The thin films investigated are all Zn-rich with respect to the stoichiometric Zn4Sb3. Their electrical resistivity decreases as film thickness increases and Zn-rich particles in the matrix grow coarse. Their Seebeck coefficient decreases as electrical resistivity decreases. Low electrical resistivity and high Seebeck coefficient can be achieved simultaneously in a film specimen with properly controlled thickness and microstructure. A nano-scale grain size in a similar to 300 nm-thick film specimen gives rise to an almost 50% reduction in its thermal conductivity. A ZT of 1.2 at similar to460 K has been obtained for a 349 nm-thick Zn4Sb3 film specimen. (C) 2003 Elsevier B.V. All rights reserved.