In this work, the essential oil of Eucalyptus citriodora was extracted and analyzed by Gas Chromatography / Mass Spectrometry. From this analysis, it appears that citronellal is the major compound (68.2%) of this oil. This aldehyde was used in situ in the essential oil of Eucalyptus citriodora for the hemi-synthesis of four structures carbazones. That was citronellal semicarbazone (1), citronellal thiosemicarbazone (2), citronellal 4-phenyl semicarbazone (3) and citronellal 4-phenyl thiosemicarbazone (4). The structures of these compounds were confirmed by IR spectrometry, proton NMR and carbon-13 and by Mass Spectrometry. From the test againstTrypanosomabruceibrucei, it appears that citronellal semicarbazone (IC50 = 473.93 μM) and citronellal thiosemicarbazone (IC50 = 440.53 μM) had low activity. Citronellal 4-phenyl semicarbazone (IC50 = 57.26 μM) and 4-phenyl thiosemicarbazone citronellal (IC50 = 19.63 μM) had moderate activity. The activity of citronellal 4-phenyl thiosemicarbazonewas still pronounced. The study of the toxicity against Artemiasalinashowed that all compounds except the compound 1were moderately toxic andmay have antitumor properties. But the most antitrypanosomal compound 4was particularly selective on trypanosome cells (SI = 4.92) and could be a good candidate against this parasite.