A systematic investigation of the light emission properties on a single ZnO microcomb structure and an individual tooth has not been carried out so far. Through a catalyst-free thermal evaporation method, we successfully synthesized large quantities of well-crystallized ZnO comb-like structures on an Si substrate. Each ZnO comb is composed of a ribbon stem and well-aligned nanotooth arrays that are evenly decorated along one side of the stem. A structural characterization reveals that the stem and the nail-like teeth, which grow respectively along the [2-1-10] and the [0001] directions, are single crystalline with a wurtzite (WZ) structure. Cathodoluminescence (CL) measurements over a single ZnO comb and a tooth were conducted to reveal a correlation between the optical properties and structural size. The results indicate an inhomogeneous light emission throughout the entire comb, and the back and tips contribute more towards the near band-edge (NBE) emission and deep level (DL) emissions than the other regions of the comb. We also observed an alteration of the relative intensity of the NBE and the DL emissions along the length of a single tooth. The middle region of the tooth, where it has the smallest diameter, shows a relatively stronger DL emission than the NBE emission. The opposite was observed at the two ends of the tooth where the diameters are larger.