In Colombia since 1984, allows the use of antibiotic growth promoters (APC) as a mechanism to improve the productive performance of poultry. but the use of subtherapeutic levels APC favors the development of antibiotic resistance factors, causing a public health problem, by the emergence of resistant bacteria. However, the use of vegetable extracts emerges as an alternative phytogenetic to the use of APC. The extract of oregano has been commonly used for its antioxidant and bacteriostatic action allowing the improvement of productive performance of broilers. The aim of this study was to evaluate the effect of the addition of fresh leaves of oregano (O. vulgare) on weight gain, efficiency and feed conversion in Cobb broilers. For this purpose we performed a study with a randomized experimental model and duration of 32 days, 8 of which were a period of adaptation to the oregano leaves feeding. Three treatments were used, each with 30 chicks of the Cobb line with independent registers and fed a commercial concentrate. The T3 is called control; the T1 and T2 were added to the commercial diet 1 and 5% respectively of fresh oregano leaves. It is observed that there is no statistically significant difference (p≥0.05) for weight gain, but if, there are statistically significant differences in the efficiency and feed conversion (p≤ 0.05) with respect to the control treatment (T3). Suggesting, that the addition of fresh leaves of oregano can improve production efficiency in poultry.