Food for feeding broilers with addition of antibiotics as growth promoters acting. Currently this is prohibited because they can transmit microbial resistance to antibiotics used in human medicine. Alternatively, the use of aromatic plant extracts, “essential oils” is proposed. To evaluate the functionality of the essential oil of oregano (AEO) (Lippia origanoides) on immunological parameters in broilers. We experimented with 200 male broilers of Avian Cobb500 line. blood samplings on 14, 28 and 42 of life. The animals were randomized to one of five diets: Commercial diet with and without antibiotic; the latter was added AEO levels (75 ppm, 100 ppm or 200 ppm). Statistical randomized block design in divided plots arrangement. Significant increase (P <0,05) in immune cell populations, significant increase (P <0,05) of post-vaccine antibodies to Newcastle and significant (P <0,05) of intestinal pH in animals fed diet with greater inclusion of AEO (200ppm) compared to the diet with antibiotic. The addition of 200 ppm of AEO stimulated immune system of birds, showing that AEO can be projected as growth promoter with immunological benefits in broilers.