Light red tomatoes were exposed to different doses of ultraviolet C (UV-C) irradiation (1.0, 3.0 and 12.2 kJ m−2). After treatment, the tomatoes were stored for 2 days at room temperature, and then analysed to determine the effect of irradiation on the main antioxidants, carotenoids and phenolic compounds and the results compared with the control samples. The lycopene content was found to have increased by 14% with respect to the control samples, while β-carotene decreased. Cis-isomers from lycopene also increased when the tomatoes were exposed to irradiation for more than 3 h. UV-C irradiation also had a positive effect on total phenolic compounds; however, the same effect was not observed in the individually analysed phenolic compounds. While chlorogenic and ferulic acids increased in content, naringenin and rutin contents decreased. These results suggest that UV-C irradiation of tomatoes could improve the beneficial effect of red tomatoes for human health by increasing the levels of certain bioactive compounds; it could also be used to obtain higher content of bioavailability components, such as cis-isomers from lycopene.