1051 tigada a concentração de extrato com efeito bioativo, pelo teste de evolução da toxicidade do extrato etanólico de J. mollissima sobre o microcrustáceo Artemia salina, obtendo uma CL50 de 660,80µg/ml, que foi testada em coproculturas contendo larvas infectantes de Haemonchus contortus e em animais para a verificação da redução do OPG. Para o teste in vivo o extrato foi dissolvido em água para se obter as concentrações 660,80µg/ml e 1321,6µg/ml, foram coletadas fezes semanalmente e sangue quinzenalmente. This study aimed to evaluate the anthelmintic effect of Jatropha mollissima through in vitro and in vivo experiments. Initially we investigated the concentration of extract with bioactive effect, through the toxicity evolution test of the ethanol extract of J. mollissima on the microcrustacean Artemia salina, obtaining CL50 concentration of 660.80µg/ml, which was tested in fecal cultures containing infective larvae of Haemonchus contortus and in animals for the verification of OPG reduction. For in vivo test, the extract was dissolved in water to obtain concentrations of 660.80µg/ml and 1321.6µg/ml. Feces were collected weekly and blood was collected every fifteen days. As a result of in vitro test, the ethanol extract of the stem of J. mollissima proved toxic on A. salina, with CL50 less than 1000µg/ ml and inhibited the eggs hatching and the development of larvae of H. contortus, presenting an efficiency of 70.77%. In vivo test revealed that the extract is also effective in sheep, with a significant reduction in the count of OPG after 28 days of experiment, 47 and 44% of reduction in the groups treated with the extract, 7.5% in the untreated group of animals and 40.6% with ivermectin. Even parasitized, the animals remained clinically healthy and without anemia. The ethanol extract of the stem of Jatropha mollissima may represent an alternative to the control of sheep worms, because it slows the parasitic resistance.