This study was aimed at determining the effect of housing systems on the growth, feed conversion ratio (FCR), meatiness and size of muscle fibres of Pekin (P44) and Muscovy (MR71) ducks. Each genetic group included 360 birds (180 males and 180 females). The ducks were divided into four experimental groups according to their sex and housing system: intensive system (IS) and outdoor system (OS). A significant effect of housing system on the final body weight and FCR value was noted only in P44 birds of both sexes, with OS birds having higher body weights than the IS birds. As a result, the OS MR71 drakes were characterized by a significantly higher slaughter yield, weight and content of breast muscles in the carcass. The OS MR71 ducks showed a lower slaughter yield and a higher content of leg muscles in the carcass compared to IS MR71 ducks. In contrast, the housing system had no significant effect on the meatiness of P44 ducks. A greater diameter of muscle fibres in both sexes of P44 ducks and in both sexes of MR71 ducks was observed in the OS compared to IS flocks. A greater cross section of muscle fibres was also noted in the ducks from the OS system, however with significant differences confirmed only in pectoralis superficialis and biceps femoris in MR71 drakes as well as in the biceps femoris of P44 drakes. These data show differences between duck genotypes and indicate the efficiency and potential of outdoor poultry systems.