ZnO optical microcavities have shown great promise as a potential core component material/structure for ultraviolet lasers, light-emitting diodes and photonic sensors because of their outstanding optoelectronic properties. Here, we report a novel ultra-thin-walled ZnO (UTW-ZnO) microtube cavity with a wall thickness of ~750 nm, supporting multiple types of optical modes, including in-tube Fabry–Perot modes, in-wall Fabry–Perot modes and wave-guided whispering gallery modes (WG-WGMs). The free-exciton recombination rate and exciton–exciton collisions are promoted in the cavity. The intensities of near-band edge (ultravoilet (UV) light) and X-band (blue light) emission are therefore increased at least one order of magnitude in the temperature range of 0–500 °C. Meanwhile, the temperature-sensitive multicolor luminescence of the UTW-ZnO microtubes in the visible band from near-white to bluish-violet is demonstrated for the first time. Low-threshold UV lasing is also achieved in the UTW-ZnO microtube by WG-WGMs, where the excitation threshold is down to 5.50 μW. Furthermore, light harvesting in the microtube cavity is beneficial to boosting the ZnO catalytic performance for photodegradation of organic dyes. The UTW-ZnO microtube exhibits compatibility to microfluidic channels for recyclable on-chip degradation. The present work provides new opportunities to design novel tubular wide-bandgap semiconductor devices for a variety of optoelectronic applications in micro/nanophotonics.