This study was conducted to investigate the effects of the sources and levels of dietary copper supplementation on broiler chickens. A 37-day feeding trial was accomplished using 192 one-day-old unsexed Arbor Acres broiler chicks which were randomly allocated into four groups with different strategies of copper supplementation. The first group was the negative control and fed on diets containing copper-free mineral-vitamin broiler premix. Diets of the second group were supplemented with copper sulfate (Cu2SO4) at the level of 7.5 mg/kg. The third and fourth groups were fed on diets supplemented with copper nanoparticles (Cu-NPs) at the levels of 7.5 mg/kg and 3.75 mg/kg, respectively. Growth performance, carcass characteristics, copper concentrations, serum antioxidant bio-markers and mRNA of metallothionein and ceruloplasmin were evaluated. Results of growth performance showed that Cu-NPs significantly (P ≤ 0.05) increased body weight gain and feed utilization compared to an equal quantity of Cu2SO4. No adverse effect on growth performance occurred when Cu-NPs were supplemented at half of the level of Cu2SO4. Dressing and thigh yields were significantly (P ≤ 0.05) increased in birds in the fourth group. Total antioxidant capacity, malondialdehyde level and transcription of ceruloplasmin were not significantly affected by the tested copper sources or levels. The superoxide dismutase enzyme activity and transcription of metallothionein were significantly (P ≤ 0.05) increased by the replacement of Cu2SO4 with the same quantity of Cu-NPs. Our findings suggested that Cu-NPs could be a superior dietary supplement of copper in broiler chickens’ diets over Cu2SO4, with possibility of quantity reduction.