Zinc oxide hexagonal microdisks with diameters ranging from 3 μm up to 15 μm were fabricated by thermal chemical vapour deposition. Optical characterisation of ZnO microdisks was performed using low temperature (80 K) cathodoluminescence (CL) imaging and spectroscopy. The microdisks exhibited green luminescence locally distributed near the hexagonal boundary of the ZnO microdisks. High resolution CL spectra of the ZnO microdisks revealed whispering gallery modes (WGMs) emission. The experimentally observed WGMs were in excellent agreement with the predicted theoretical positions calculated using a plane wave model. This work could provide the means for ZnO microdisk devices operating in the green spectral range.