A study was designed to investigate the effect of different levels of dietary nano zinc oxide (NZnO) on growth performance, carcass traits, digestive tract measurements, immune response and economic efficiency of broiler chicks. A total number of 192 unsexed day-old "Cobb" broiler chicks were distributed in a completely randomized design of six treatments with four replicates (8 chicks each). The control (T1) contained 100 mg inorganic zinc oxide (IZnO)/kg of diet. Treatments two to six contained 100, 80, 60, 40 and 20 mg NZnO/kg of diet, respectively. No significant differences were observed between treatments on growth parameters except for feed conversion ratio (FCR) and performance index (PI). However, birds fed 40 mg NZnO (T5) consumed less feed and recorded the highest LBW, TBWG and the best CPC and CCR compared with the other treatments. The best FCR (P≤0.01), PI (P≤0.05), economic efficiency (EE) and the relative EE were obtained by T5. The highest (P≤0.05) breast and thigh (P≤0.01) and the lowest abdominal fat percentages were observed with birds fed the control and T6 (20 mg NZnO) compared to other treatments. Thymus percentage was reduced (P≤0.01) by T5 compared with control, T3 and T4 while the bursa percentage was increased by T4 and T5 compared with the other treatments. It could be concluded that NZnO at a level of 40 mg/kg of diet had no harmful effect on health status and could be used instead of the traditional zinc sources in broiler diets.