This experiment was conducted to study the influence of feeding a natural feed additive, Nigella sativa seeds (NS), at different levels on growth performance, carcass characteristics and economic efficiency of broiler chicks. One hundred and forty unsexed one-day-old Arbor Acres broiler chicks were battery reared in a semi-open house. Chicks were assigned into four treatment groups. Each treatment consisted of seven replicates each replicate contained five birds. The first diet was the control without NS. The second, third and fourth diet were supplied with 0.5, 1.0 and 1.5% Nigella sativa, respectively. Results showed that the addition of NS at 0.5, 1, and 1.5% levels induced higher market body weight and body weight gain compared to the control group. Moreover, NS supplementation significantly (P<0.05) increased ether extract and crude fiber digestibility compared to the control group. Carcass weight percentage increased (P<0.05) due to feeding NS at different levels ranged between 74.7 to 76.5% compared to the control group (66.4%). In addition, Bursa of Fabricius and heart weight percentages were higher than those of the control group at 1 and 1.5% NS levels. Broiler chicks fed diets supplemented with 0.5% and 1% NS were more economical than the control group. They showed a high increase in total revenue, net revenue and relative economic efficiency percentages. It could be concluded that the addition of NS up to 1% seems to have a positive effect on growth, carcass characteristics and economic performance, moreover, it can be used as a growth promoter feed additive for broiler chicks.