Abstract: Several factors may affect poultry breast meat quality, both intrinsic characteristics (age, sex, size and strain) and external influences (carcass aging time postmortem before deboning, fillet marination and cooking method). Commercial duck processors are now expanding into the deboned breast meat markets but very little research is available on duck meat quality as compared to other poultry species. Therefore, the following study was conducted to determine the effect of duck sex, size and fillet marination on breast meat quality. Duck rearing, processing and carcass deboning were conducted at a commercial facility. Carcasses were kept separate by sex and were then sized to 1.6 kg (S), 2.0 kg (M) and 2.5 kg (L) after chilling. After 6 h aging on the carcass, breast fillets were removed and half of the fillets from each sex-size category were marinated while the other half of the fillets (unmarinated) were held as controls. A total of 360 fillets were produced, 30 in each of 12 categories (2 sexes X 3 sizes X 2 treatments). At the laboratory, fillets were weighed, evaluated for raw color, cooked, reweighed, evaluated for cooked color and sheared via Warner-Bratzler (WB). Uncooked and cooked fillet weights were significantly affected by bird size (p<0.05). Marination increased fillet cook yield compared to control fillets (73.5% versus 69.1%, respectively) and decreased WB shear values (2.2 kg versus 3.2 kg, respectively). Less force was required to shear the first slice using WB as compared to the second WB slice (2.4 and 3.0 kg, respectively). Lightness (L*) and yellowness (b*) values were lower in uncooked fillets from females than males ducks and marination decreased raw fillet L* values and cooked b* values for both sexes. Results showed that sex, carcass size and marination affect duck breast meat quality.