The chloroformic extracts from dried fresh leaves ofAzadirachta indica A. Juss. and Melia azedarach L. (Meliaceae) showed marked inhibitory activity on epimastigotes growth of Trypanosoma cruzi, evidenced by 96-wells microtiter plate bioassay and radioactive thymidine incorporation experiment. Each chloroformic extract was separated using silica gel and alumina column. In transmission electron microscopy the bioactive chromatographic fractions caused ultrastructural changes in epimastigotes such as vacuolization probably induced by degeneration of the kinetoplast-mitochondrion complex, organelle degeneration, and cell division disruption. In spectral analysis these bioactive fractions seemed to be composed mainly of fatty acid mixtures.