Aim The aim of this study was to examine if erythropoietin (EPO) has the potential to act as a biological antioxidant and determine the underlying mechanisms. Methods The rate at which its recombinant form (rHuEPO) reacts with hydroxyl (HO˙), 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH˙) and peroxyl (ROO˙) radicals was evaluated in‐vitro. The relationship between the erythopoietic and oxidative–nitrosative stress response to poikilocapneic hypoxia was determined separately in‐vivo by sampling arterial blood from eleven males in normoxia and following 12 h exposure to 13% oxygen. Electron paramagnetic resonance spectroscopy, ELISA and ozone‐based chemiluminescence were employed for direct detection of ascorbate (A˙−) and N‐tert‐butyl‐α‐phenylnitrone spin‐trapped alkoxyl (PBN‐OR) radicals, 3‐nitrotyrosine (3‐NT) and nitrite (NO2−). Results We found rHuEPO to be a potent scavenger of HO˙ (kr = 1.03–1.66 × 1011 m−1 s−1) with the capacity to inhibit Fenton chemistry through catalytic iron chelation. Its ability to scavenge DPPH˙ and ROO˙ was also superior compared to other more conventional antioxidants. Hypoxia was associated with a rise in arterial EPO and free radical‐mediated reduction in nitric oxide, indicative of oxidative–nitrosative stress. The latter was confirmed by an increased systemic formation of A˙−, PBN‐OR, 3‐NT and corresponding loss of NO2− (P < 0.05 vs. normoxia). The erythropoietic and oxidative–nitrosative stress responses were consistently related (r = −0.52 to 0.68, P < 0.05). Conclusion These findings demonstrate that EPO has the capacity to act as a biological antioxidant and provide a mechanistic basis for its reported cytoprotective benefits within the clinical setting.