Visceral leishmaniasis is caused by parasites of the genus Leishmania. Prevalent in developing countries, the disease is on the list of the world’s most neglected diseases. Most cases (90%) in Latin America occur in Brazil, especially in the Northeast. The condition is treated mainly with pentavalent antimonials, an expensive and relatively inefficient drug known to induce resistance. In search of new antileishmanial drugs, much attention has been given to the medicinal properties of coumarin. In this study, coumarin was isolated from seeds of Amburana cearensis, purified and evaluated with regard to its ability to inhibit Leishmania chagasi promastigotes using the MTT test. The cell viability of macrophages treated with coumarin was also evaluated. The findings were submitted to one-way ANOVA for paired data, followed by the Bonferroni correction. The level of statistical significance was set at 5% (p < 0.05). Coumarin displayed low toxicity to macrophages in the MTT test (p > 0.05), but was toxic to Leishmania chagasi promastigotes (p < 0.05). Our results represent a contribution to the development of new drugs for the control or prophylaxis of visceral leishmaniasis.