Introduction. Red-purple pitahaya (Hylocereus sp.) is a promising crop grown commercially in dry regions of Central America. Both its skin and flesh are characterized by being a glowing, deeply red-purple color. Materials and methods. The main physicochemical characteristics of three commercial cultivars of red pitahaya were assessed, including total phenolic compounds contents, total betacyanins, vitamin C and oxygen radical absorbance capacity (ORAC). Thermal stability of betacyanins at different temperature and pH was also assessed. Results and discussion. Pitahaya fruit has a low vitamin C content ranging from (116 to 171) µg·g–1 of fresh pulp without seeds, but it is rich in betacyanins [(0.32 to 0.41) mg·g–1] and phenolic compounds [(5.6 to 6.8) µmol Eq gallic acid·g–1]; it has a high antioxidant ORAC value of (8.8 to 11.3) µmol Eq Trolox·g–1. Visible spectra of aqueous fruit extracts were very similar to that of pure betacyanin. Indeed, the characteristic color of juice diluted to 1% presents a high hue angle (H° = 350º ± 3) and high chroma values (C* = 79 ± 2). Thermal stability of pitahaya betacyanin decreases with pH, but it remains compatible with industrial utilization as a colorant (half-time = 22.6 min at 90 °C at pH = 5 of the fruit) and was found to be very similar to that previously reported for beetroot. Conclusions. Pitahaya juice combines the functional properties of a natural food colorant with high antioxidant potency.