The widespread use of antibiotics as growth promoters and for disease prevention in poultry production has been caused to development of antibiotic resistance. Therefore, the use of antimicrobial growth promoters has been forbidden in the European Union since 2006 [1]. Nowadays, many phytogenic plans have been evaluated and tested as alternatives to chemical antibiotics for poultry [2]. Oregano with the scientific name Mentha longifolia is a medicinal plant of Laminaceae family which is used in traditional medicine for treatment of nausea, Bronchitis, bloat, anorexia, colon ulcers and digestive and hepatic disorders [3]. Also, oregano is a plant grown for culinary purposes and generally improves the organoleptic characteristics of food [4]. Thymol and Carvacrol are the two main Phenolic compounds which constitute up to 80% of oregano essence and are responsible for its antioxidant activities and have been recognized as potent antimicrobial compounds [3]. It has been reported that the dietary oregano powder supplementation significantly (P<0.05) increased average daily feed intake and body weight gain of broilers during grower and entire production period [2]. In this study, a total of 480 one-day old Ross 308 broiler chicken were randomly allocated to 6 treatments, 5 replicates and 16 birds in each replication. The experimental treatments included control (with no feed additive), 0.02% Virginiamycin as growth promoter antibiotic, and 0.25%, 0.50%, 0.75% and 1.0% oregano powder. Feed intake, body weight, body weight gain, and feed conversion ratio (FCR) were recorded weekly. The data were analyzed in a completely randomized design using the GLM procedure of SAS. Comparison of means was conducted by Duncan's multiple range rest. The results of the present study showed that in different and also whole experimental period, the use of 0.25% and 0.50% dietary oregano powder significantly (P<0.05) increased feed intake and body weight gain whereas the utilization of 1.0% d
