The hypothesis was that owing to their high bioavailability, zinc oxide nanoparticles (NanoZnO) can effectively replace (Zn) salts and reduce Zn excretion with faeces. The objective of this study was to investigate the effects of NanoZnO on the development of chicken embryos, the growth of broiler chickens, and Zn excretion with faeces. At day 1 of incubation, 120 eggs were randomly divided between a control group (not injected) and groups injected with a hydrocolloid of NanoZnO in increasing concentrations (50, 100, 500 mg/L). At day 19 of incubation, no differences were observed in the bodyweight, but 100 and 500 mg/L affected liver and heart weights, indicating that high levels of NanoZnO may induce differential organ development. In the subsequent experiment, 308 chickens were randomly divided into six groups. The control diet was supplemented with 55 mg Zn/kg (standard level), the 0 group received no Zn supplement, and groups fed NanoZnO received 25%, 50%, 75%, and 100% of the standard level. The 100% replacement of ZnO with NanoZnO increased the chickens’ bodyweight compared with the standard level of ZnO, but to the same level as the diet without ZnO supplementation. Furthermore, NanoZnO did not reduce the content of Zn in faeces, which was only significantly lower in the group without ZnO supplementation in comparison with other groups. The results indicate that the replacement of ZnO with NanoZnO had no negative effects on chicken growth. Compared with ZnO, NanoZnO did not reduce Zn excretion with faeces.