A series of eleven 3,4-methylenedioxyde-6-X-benzaldehyde-thiosemicarbazones (16-27) was synthesised as part of a study to search for potential new drugs with a leishmanicidal effect. The thiosemicarbazones, ten of which are new compounds, were prepared in good yields (85-98%) by the reaction of 3,4-methylenedioxyde-6-benzaldehydes (6-X-piperonal), previously synthesised for this work by several methodologies, and thiosemicarbazide in ethanol with a few drops of H2SO4. These compounds were evaluated against Leishmania amazonensis promastigotes, and derivatives where X = I (22) and X = CN (23) moieties showed impressive results, having IC₅₀ = 20.74 μM and 16.40 μM, respectively. The intracellular amastigotes assays showed IC₅₀ = 22.00 μM (22) and 17.00 μM (23), and selectivity index >5.7 and >7.4, respectively, with a lower toxicity compared to pentamidine (positive control, SI = 4.5). The results obtained from the preliminary QSAR study indicated the hydrophobicity (log P) as a fundamental parameter for the 2D-QSAR linear model. A molecular docking study demonstrated that both compounds interact with flavin mononucleotide (FMN), important binding site of NO synthase.