Copper is a vital trace element involved in various physiological and biochemical processes. However, animals can only absorb a small fraction of copper and the most is excreted, contaminating soil and aquatic environment. Hence the use of this mineral as a growth promoter is today one of the crucial health and environmental concerns. In recent years, many studies have reported copper nanoparticles (Cu-NP) as a promising alternative to antibacterial reagents and a growth promoter. Depending on the size, shape, dose and animal species, Cu-NP exhibit a variety of effects on animal performance. Apart from being highly bioavailable, reports have already pointed out the growth-promoting, antibacterial and immune-modulatory effects of Cu-NP. Toxicological studies provide varied results in animal models. However, other studies being undertaken in different animal species have shown the promise of Cu-NP supplementation. Therefore, there is a need to optimise the dose and duration of Cu-NP supplementation for livestock, depending on their biological effects. Moreover, the bioavailability of Cu-NP in livestock still needs further confirmation. In this review, we summarise the benefits and hazardous effects of Cu-NP and the possibility of using Cu-NP as a feed supplement in different animals in general and in poultry particularly.