Context: Asthma is characterized by hyperresponsiveness and bronchoconstriction, induced by histamine and other noxes, with a prevalence in Peru of 20.7-28.2%, which is why, in traditional medicine, Jatropha macrantha Müll.Arg is used. Aims: To evaluate the in vivo bronchodilator activity of the ethanolic extract of the stems of J. macrantha. Methods: The powdered material of the stem of J. macrantha was extracted with ethanol 96° by maceration; then, the phytochemical screening was carried out. The doses of 200, 400 and 800 mg/kg of the extracts were subjected to in vivo evaluation in guinea pigs (Cavia porcellus) with 1% histamine-induced bronchoconstriction, determining the latency period and the intensity of the effect. Results: Phytochemical sieving showed alkaloids, catechins, flavonoids, tannins and terpenes. The activity was observed at the three doses of the J. macrantha extract, being higher at a single dose of 400 mg/kg, with a latency period of 33.0 ± 1.02 s, asphyxia 84.5 ± 1.08 s and anaphylaxis 105.6 ± 0.59 s. The analysis of variance and Dunnett's test resulted with p<0.05 as statistically significant. Conclusions: The results showed bronchodilator activity of the ethanolic extract of J. macrantha at an average dose of 400 mg/kg, orally, in Cavia porcellus.