This paper studies the effect of synthesized zinc oxide (ZnO) on the heating time and aluminium oxide (Al2O3) doped with ZnO on the structural and optical properties. The heating times are 20, 30, 40, 50 and 60 min prepared using the hydrothermal method. Other samples are Al2O3 doped with ZnO at 0, 0.5, 1.0, 1.5 and 2.0 mol% also via hydrothermal method. The characterization of the samples used XRay Diffraction (XRD) and UV-visible (UV-vis) spectroscopy to study the structural and optical properties. From the XRD results, we can see that the heating times for 20 to 60 min doesn't form crystallite, while for doping with Al2O3 the samples show the hexagonal wurtzite structure with high crystallinity. From XRD result, the data shows the crystallinity increases for Al2O3 doped with ZnO. UV-vis spectroscopy shows that the absorption peak is in the range 200-800 nm for all samples. UV-vis spectrum shows that the ZnO has a small peak at 300-400 nm for different heating times, while for doping with Al2O3 in ZnO samples, there have no peak. All samples shown the lower peaks in UV-vis spectrum explained that samples are formed as opaque. This study showed that the high crystallinity structure does not show the affected on the optical properties. Copyright (c) 2021 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 3rd Symposium on Industrial Science and Technology 2021