An experiment was conducted in the poultry farm of Al-Shouback University College in the campus of Al-Balqa` Applied University to evaluate the effect of using a medicinal plant seed powder of black cumin (Nigella sativa L.) as a natural feed additive on the performance of 4-8 week-old broilers. Two hundred and forty growing broilers at 4 weeks of age were weighed and randomly distributed into four treatments, with 3 replicates. The seed powder of N. sativa was daily prepared and mixed with the broiler’s finisher diets at rates of 1.0, 1.5 and 2.5% per km of broiler’s finisher diet. Control group received a complete finisher diet free of N. sativa seed powder and any additive. The experimental diets of N. sativa seed powder were offered Ad libitum during the age 4-8 weeks of lohman broilers reared in an open-sided poultry house. The results showed that, feeding of the diets with 1 and 1.5% N. sativa seeds for a period of 4 weeks was significantly (pN. sativa had significantly (pN. sativa in their diet. Increasing the feeding rate of N. sativa up to 2% was associated with a significant (pN. sativa seeds in the diet reduced the cumulative rate of mortality. Based upon this study, it could be concluded that using the medicinal seed powder of black cumin ( Nigella sativa L.) as a natural feed additive at a rate of 1.5% revealed positive effects on the performance and survivability of broilers grown at normal conditions in an open sided environment.