Changes of morphology during the growth of ZnO on Al 2 O 3 (0001) substrates by metalorganic chemical vapor deposition (MOCVD) were investigated as a function of growth temperature (T g ). The morphology of ZnO changes dramatically with T g . At very low growth temperatures of T g ⩽200°C, no meaningful ZnO forms. At 200°C<T g ⩽260°C, columnar grained, textured ZnO films having a large amount of crystalline defects grow. At higher growth temperatures of 260°C<T g ⩽320°C, arrays of vertically well-aligned ZnO nanorods grow. The nanorods are aligned epitaxially with a 30° rotation of ZnO basal planes with respect to Al 2 O 3 basal planes. At further higher growth temperatures of 320°C<T g ⩽380°C, ZnO of nanoneedle type grows. However, at T g >380°C, ZnO nanowires start to grow on top of a continuous ZnO layer. Both the nanoneedles and the nanowires are not only well aligned both in the out-of- and in the in-plane direction, but also show a very low density of crystalline defects. Our results suggest that T g is one of the key processing parameters and need to be optimized in a narrow regime in order to grow a desired type of ZnO in MOCVD process.