This study was conducted to investigate the effect of supplementing broiler chicken diets with a blend of plant extracts on the growth performance, serum lipid profile, humoral immune response against Newcastle disease virus vaccines and carcass traits. Methodology: The plant extract blend was supplemented in the diets as a natural growth promoter at five different levels (100, 200, 500, 1000 and 2000 ppm). Broilers fed on the plant extract supplanted diets were compared to those fed on the un-supplemented (negative control) and antibiotic (oxytetracycline) supplemented (positive control) diets making seven dietary treatments. Results: Inclusion of the plant extract blend at levels of 200 and 1000 ppm resulted in a significant improvement in the overall performance parameters compared to the negative control. The best results were observed in broilers fed on the positive control diet. No significant differences were found between broilers fed on the positive control and those fed on 200 and 1000 ppm of the plant extract blend. Dietary intake of the plant extract blend, but not oxytetracycline resulted in a significant increase in the humoral immune response. No differences were observed among treatments in the measured serum lipid parameters or carcass traits (p>0.05). Conclusion: The tested extract blend can be utilized at a level of 200 ppm as an alternative to antibiotic growth promoters and to improve broiler performance and immune response.