Background: The prohibition of the use of antibiotics in lamb feeding requires the search for natural alternatives that can improve productive performance and ruminal fermentation parameters. Herbal mixtures can function as cost-effective substitutes for growth promoters since an extraction or purification process is not required. Methods: An experiment was conducted to evaluate the effect of Chebulic myrobalan, Terminalia bellirica and Azadirachta indica on the productive performance of finishing lambs. Thirty-six Hampshire x Suffolk male lambs (initial body weight (BW) 23.52±3.67 kg), in individual crates, were used for 45 days of evaluation after 15 days adaptation and were randomly assigned to treatments which consisted of dietary inclusion of the feed plant additive at 0.000, 0.250, 0.375 and 0.500% of dry matter (DM). Rations were sampled for DM, ash and crude protein (AOAC, 2005), neutral and acid detergent fibre (according to van Soest, 1991) analysis and metabolizable energy was estimated. The animals were weighed on days 1, 15 and 45 before feeding and the average daily gain (ADG) and feed conversion rate were calculated by daily recording of the dry matter intake. Contrasts no orthogonal were used to test linear or quadratic effects of the herbal mixture with initial body weight (BW) as a covariate for ADG and final BW. Result: There was no effect (P greater than 0.05) of herbal mixtures on ADG, final BW, feed efficiency, DM intake and feed conversion by phytobiotic dietary inclusion. Ruminal pH (P=0.07) increased quadratically in response to the herbal mixture dietary concentration. The acetate increased and propionate reduced, both quadratically (P less than 0.05). The evaluated doses of the polyherbal additive did not influence growth and feed efficiency of lambs.