ABSTRACT. Avelar, B. R., Lambert, M.M, Siqueira, R.C.S., Cid, Y.P., Chaves, D.S.A., & Coumendouros K. [In vitro activity of essential oils and extracts from Schinus molle L. against Rhipicephalus microplus]. Atividade in vitro de óleos essenciais e extratos de Schinus molle L. frente a Rhipicephalus microplus. Revista Brasileira de Medicina Veterinária, 38(supl. 3):218 - 228, 2016. Programa de Pós-Graduação em Ciências Veterinárias, Instituto de Veterinária, Anexo 1, Universidade Federal Rural do Rio de Janeiro, Campus Seropédica, Ecologia, BR 465 Km 7, Seropédica, RJ 23897-970, Brasil. E-mail: firstname.lastname@example.org The aim of the study was to evaluate the in vitro activity of Schinus molle L. extracts (hexane, ethyl acetate and methanol) and essential oils (leaves and fruit) on different evolutionary forms of Rhipicephalus microplus. The immersion test using engorged females was used (Drummond et al., 1973). The extract were obtained from leaves of S. molle by soxhlet and diluted in the concentration ranges between 20,000 and 1,250 ppm (parts per million), and positive and negative controls were used. The S. molle hexane extract showed efficacy in vitro of 57,7% in concentration of 1.250 ppm while other extracts and essential oils showed no significant inhibition.