A 49 days experiment was conducted to evaluate the effects of different levels of rosemary leaves (RML) or black seeds (BS) powder, as natural feed additives, on growth performance, carcass traits and some blood plasma constitutes of broiler chicks. A total of 210 one-day-old unsexed Hubbard chicks were divided into seven treatments of three replicates of ten chicks each. Treatments were 0.25, 0.50, 0.75 and 1.0% (RML), 0.50 and 1.0% (BS) and no additives (control). Supplementation of RML (up to 0.5%) and BS (up to 1.0%) increased birds body weight (BW) at all ages; the highest final BW was obtained by 0.5% RML and 1.0% BS in comparison with the rest of the treatments. A reduction in BW was noticed with increasing RML levels over 0.5%. All various contrasts of treatments vs. control did not show any significance in average daily gain or feed intake. Significant feed, crude protein and caloric conversion ratios were obtained by 0.5% RML vs. control during the total period. Most dietary RML or BS levels versus control significantly improved the livability and the European production efficiency factor. No significant effects on most carcass traits, plasma total protein and total lipids were detected. Plasma total cholesterol was decreased by 0.75 RML and 1.0% BS compared to 0.25% RML. A significant reduction in plasma triglycerides by 1.0% RML vs. control was reported. All treatments (except 1.0% RML and 0.5% BS) significantly increased plasma uric acids. A significant increment in percentages of bursa by RML (0.25 and 1.0%) vs. control and in spleen by RML (0.75 and 1.0%) was noticed. Supplementation of 0.5% RML and 1.0% BS significantly reduced abdominal fat percentage compared with the control. It was concluded that 0.5% RML and 1.0% BS, as natural feed additives, enhanced broilers performance.