Pitaya (Stenocereus griseus) juice, obtained from fresh pitayas, was processed using a continuous ultraviolet-C (UV-C) light (57 µW/cm²) system. Juice was processed at five flow rates (0.46, 3.28, 6.57, 16.49 and 30.33 mL/s) and five treatment times (5, 10, 15, 20, and 25 min). Fresh juice was used as control. Some physicochemical (pH, total soluble solids, color, and betalains), antioxidant (total phenolic compounds and antioxidant activity), and microbiological (aerobic mesophylls bacteria and yeasts plus molds) characteristics were assessed in fresh and UV-C processed juices. It was observed that the UV-C treatments did not affect pH and total soluble solids in juice. The total change in color (DE) increased as treatment times increased; however, DE values were reduced at high flow rates. The betalains and total phenolic compounds contents were reduced as flow rates and treatment times increased; consequently, the antioxidant activity lessened in juice. A maximum reduction of 2.11 and 1.14 log cycles was observed for mesophylls and yeasts plus molds, respectively, in the UV-C light treated pitaya juice.