Zn 0.3 In 1.4 Sn 0.3 O 3− δ (ZITO) thin films were grown by computer-controlled pulsed laser deposition (PLD) on (0001) Al 2 O 3 substrate. Cross-section and plan-view transmission electron microscopy (TEM) revealed that the ZITO films were composed of twin-related domains with their (222) planes parallel to (0001) planes of the Al 2 O 3 substrate. ZITO {55¯0} planes fitted well to Al 2 O 3 {33¯00} planes with a lattice mismatch of approximately 2.8%. Remarkable enhancement of electrical conductivity, about one order of magnitude higher than that of bulk ZITO, was found. The formation of twin-related domains and its effects on electrical and optical properties of ZITO films were also discussed.