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Comets and asteroids hold important clues about the history of our solar system, and studying their volatiles and surfaces can provide valuable insights. Ultraviolet (UV) observations have proven effective for this purpose, but limited by Earth's atmosphere and low UV brightness of small bodies. Therefore, we conducted new UV observations using the Ultraviolet and Optical Telescope (UVOT) on board the Neil Gehrels Swift Observatory (Swift) and analysed archived ones to improve our understanding of cometary volatiles and asteroid surface evolution. Specialized observation strategies and data processing techniques were designed and applied to three observation campaigns. First, water activities of the first discovered active interstellar comet 2I/Borisov were detected. The results show that the comet neither stands out exceptionally from solar system comets, nor fits neatly into any class of them. Second, spectra of an asteroid survey were analysed. They generally connected the results observed by other instruments and filled the critical near-UV spectral gaps for studying space weathering. Finally, we observed the largest outbursts of the comet 29P/Schwassmann-Wachmann 1 without discovery of UV emissions of any gas in the coma. The activity mechanisms need to be further examined.