In order to take the advantages of the anticancer properties of benzimidazoles and hydrazones, we synthesized new 4-(5-chloro-1H-benzimidazol-2-yl)-benzoic acid benzylidene hydrazide derivatives (3a-3t) and evaluated their anticancer activity against A549 (human lung adenocarcinoma) and MCF-7 (human breast adenocarcinoma) cells. The structures of the compounds (3a-3t) were confirmed by IR, H-1-NMR, C-13-NMR, mass spectroscopy, and elemental analyses. Antiproliferative activities of the compounds were evaluated using MTT assay, BrdU method, and flow cytometric analysis. In addition, with purpose of determining selectivity the cytotoxic activities of the final compounds were screened against healthy NIH3T3 cell line (mouse vembryonic fibroblast cells). Among the tested compounds 3e and 3f showed significant cytotoxic activity against A549 and MCF-7 cancer cells with an IC50 value of 0.0316M. Furthermore, compound 3p showed remarkable cytotoxic activity against MCF-7 comparing with standard drug cisplatin. Annexin V-FITC assay also suggested that this compounds induced cell death by apoptosis.