Novel benzimidazolium bromides salts having (4-methoxyphenyl)ethyl, (phthalimide-2-yl)methyl, 4-nitrobenzyl, 2-phenylethyl, penthyl, or allyl groups were synthesized and their characterizations were conducted by H-1 and C-13 NMR and IR spectroscopic methods, and microanalysis. In vitro antitumor activities of the novel benzimidazole compounds (1-7) were determined by using ovarian (A2780) and prostate (PC-3) cancer cell lines. Antitumor properties of all compounds were determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MIT) assay. A time-dependent cell viability assay for the tested benzimidazole compounds was performed and the IC50 values of the compounds were calculated after treatment for 24 and 48 h. Our results indicate that the tested benzimidazole compounds show antitumor activity against A2780 and PC-3 cell lines (P < 0.05).