Leishmania parasites cause a worldwide public health disease and its treatment is still based on pentavalent antimonials which present financial and toxicologic limitations. Some nucleosidic derivatives have demonstrated anti-leishmanial properties and this study aims to evaluate the in vitro morphologic alterations and growth inhibition of Leishmania (L.) amazonensis promastigotes exposed to zidovudine at several concentrations. The citotoxicity of zidovudine (AZT) to macrophages was determined by an MTT assay. After which the promastigotes were exposed to concentrations of AZT, ranging from 1 to 50 μM. The evaluation of survival and morphometry alterations were performed in two distinct phases of in vitro growth, on the third and sixth days, representing the logarithmic and stationary phases, respectively. Slides with the promastigotes were photographed and analyzed using Image J. A significant reduction of parasite number in the logarithmic phase of in vitro growth was observed when the parasites were submitted to 20, 30, 40, and 50 μM of AZT. Morphometric alterations were observed such as an increase in width of the body, cytoplasmic granulations and vacuolizations. These data indicate the toxicity of AZT which prevents the parasite's multiplication, indicating a promising use of AZT as an anti-leishmania drug.