The objective was to evaluate the efficacy of hydro-alcoholic extracts of nim and citronela at 20% and eucalipto at 10% in Boophilus microplus engorged females collected in cattle naturally infected from the mesoregion West of Maranhão. At the laboratory the females were separated, weighted and distributed in six groups of 10, in duplicate. Each group was immersed in 10mL of the solution of the extracts, for two minutes. In the nim and citronela extracts there was 32% e 17%, respectively, while larval emergence the eucalipto extracts demonstrated 96% of efficacy. In the groups treated by Cipermetrina + Clorpirifós + Citronetal and Deltametrina (positive controls) the mortality occurred after 48h of treatment, while the groups immersed in distilled water (negative control) showed 100% of eggs mass and larval emergence. According to the results, it can be concluded that the extract of eucalipto could be used as acaricide in the control of B. microplus females since it was efficient in vitro, however to nim and citronela showed not efficacy. B. microplus females were not resistant to the chemical compounds used in this experiment.