Plumage ornaments such as the house sparrow (Passer domesticus) badge are often associated with traits correlated with fitness. For example, in several avian species, males with higher saturated red colored plumage and/or darker melanistic characteristics have better body condition, higher levels of antioxidant capacity, and greater over winter survival and lifetime reproductive success. The mechanisms that link these plumage characteristics with traits associated with fitness are not fully clear. Recently mitochondrial copy number (mtDNAcn) has been found to be positively correlated with oxidative damage and antioxidant capacity, related to disease prevalence in humans, and egg and sperm quality in captive mammals. In male house sparrows, badge size is positively related to proportion of offspring fledged, and in other bird species brood size and oxidative stress were positively correlated. Together, this suggests a potential link between badge size and mitochondrial-related metabolic processes and by-products that may influence fitness. Here we test the hypothesis that the melanistic-based badge trait in house sparrows is associated with mtDNAcn and total plasma antioxidant capacity, as well as, the relationship between these traits and reproductive fitness. To investigate this hypothesis, blood samples from male house sparrows were collected during chick rearing to assess mtDNAcn and total plasma antioxidant capacity. Badges were photographed to quantify badge size and color saturation. We predict males with larger and darker badges will have higher levels of total antioxidant capacity, mtDNAcn and fledging success. This data will provide a potential underlying mechanistic linkage between ornamentation and reproductive fitness.