Photodegradation by ultraviolet irradiation (UV) is increasingly applied in volatile organic compound (VOC) and odor gas treatments. In this study, 27 typical VOCs, including 11 hydrocarbons and 16 hydrocarbon derivatives, at 150–200 ppm in air and nitrogen gas were treated by a laboratory-scale UV reactor with 185/254 nm irradiation to systematically investigate their removal and conversion by UV irradiation. For the tested 27 VOCs, the VOC removal efficiencies in air were within the range of 13%–97% (with an average of 80%) at a retention time of 53 s, which showed a moderate positive correlation with the molecular weight of the VOCs ( = 0.53). The respective contributions of photolysis and photooxidation to VOC removal were identified for each VOC. According to the CO results, the mineralization rate of the tested VOCs was within the range of 9%–90%, with an average of 41% and were negatively correlated to the molecular weight ( = 0.63). Many of the tested VOCs exhibited high concentration particulate matters in the off-gases with a 3–283 mg/m PM range and a 2–40 mg/m PM range. The carbon balance of each VOC during UV irradiation was analyzed based on the VOC, CO and PM concentrations. Certain organic intermediates and 23–218 ppm ozone were also identified in the off-gases. Although the UV technique exhibited a high VOC removal efficiency, its drawbacks, specifically low mineralization, particulate matters production, and ozone emission, must be considered prior to its application in VOC gas treatments.