Small libraries of bisbenzimidazoles structurally related to pentamidine have been synthesized and evaluated against different species of parasites. 2,2’-[1,3-Propanediylbis(oxy-1,3-phenylene)]bis-1H-benzimidazole emerged as a potent and selective anti-Trichomonas vaginalis agent from in vitro and in vivo studies. In particular, in vitro under aerobic conditions the compound was more active than metronidazole against both metronidazole-susceptible (C1) and –refractory (085) isolates of Trichomonas vaginalis. In vivo, it cured a subcutaneous mouse model infection using both kinds of isolates.