ZnO nanorods with various diameters were synthesized on both sapphire and silicon substrates by a pulsed-laser-deposition technique without a catalyst using relatively high background oxygen pressure (5–20 Torr) and substrate temperature (550 °C-700 °C). The photoluminescence (PL) properties of the nanorods were investigated. The difference in PL emission intensity for the samples produced at various oxygen pressures has been attributed to the size difference and surface status of the nanorods. The increased deep level emission with increasing temperature resulted from the size difference and increasing oxygen evaporating. The effect of substrate nature on the PL property has also been investigated.