The aim of this experiment was to determine whether the inclusion levels of supplemental copper (Cu) in turkey diets can be decreased without compromising important metabolic functions, growth parameters and carcass quality, and whether the above goals can be achieved with the involvement of Cu nanoparticles. The experiment was carried out on 648 one-day-old Hybrid Converter turkeys divided into 6 groups, with 6 replicates per group (18 birds per replicate). The experiment had a two-factorial design, with Cu sulphate (Cu-SUL) and Cu nanoparticles (Cu-NP) as 2 dietary sources of Cu, and 3 dietary inclusion levels of Cu (2, 10 and 20 mg/kg). It was demonstrated that the replacement of Cu-SUL with Cu-NP and a decrease in a dose of supplemental Cu from 20 to 10 mg/kg or even 2 mg/kg of the diet did not affect the growth parameters or the carcass quality of turkeys. The few effects exerted by the substitution of Cu-SUL with Cu-NP included an increase in haemoglobin levels and an improvement in the antioxidant status of fresh breast meat. However, fresh meat was characterised by optimal redox parameters when the dietary dose of Cu was decreased to 10 mg/kg. The results of the present study cannot be generalised, but they significantly expand the knowledge about Cu-NP as an efficient source of Cu for turkeys.