Background: Benzimidazole constitutes a starting point for the development of new antiprotozoal agents since this nucleus exists in several pharmacologically significant molecules, in particular possessing antifungal, antiviral, antibacterial, and antiparasitic properties. Objective: The present study aimed to identify a molecular hit likely to be developed as an anti-leishmanial and antitrypanosomal drug candidate. Methods: Thus, 12 hybrids of chalcone or benzimidazolyl-arylpropenones were synthesized and screened in vitro for anti-leishmanial activity against promastigotes of Leishmania donovani. The microculture tetrazolium assay was used to determine their potential to inhibit 50% of a parasite growth (IC50). Results: Two compounds among 5-chlorobenzimidazole-chalcones (4a and 4c), which exhibited potent activity (IC5050 μM) were selected to check their trypanocidal activity. Lethal concentration (LC100) values of these compounds were estimated by using observations on the viability of trypomastigotes of Trypanosoma brucei brucei in MEM medium with Earle’s salts and L-glutamine. Seven of the tested compounds (4a, 4b, 4c, 4e, 4g, 4h, and 4j) showed particularly higher inhibitory activity than pentamidine (IC50= 7.6 μM) against L. donovani promastigotes with IC50 values in a range from 0.5 to 1.8 μM. In addition, the 2’-chlorine derivative (4c), displayed potent anti-trypanosomal activity comparable to those of melarsoprol, used as reference drug. Conclusion: These results support this series of benzimidazole holding arylpropenone group in position 2 as a starting point for future optimization to get novel agents active against leishmaniasis and trypanosomiasis.