A library of twenty-four, structurally diverse, 2-substituted and 1,2-disubstituted benzimidazole derivatives (4a-x) was designed and synthesized. The benzimidazole derivatives were constructed by a one-pot condensation reaction between 1,2-phenylenediamines and aromatic aldehydes under mild oxidation conditions utilizing inexpensive and non-toxic inorganic salt sodium metabisulfite. These compounds were assayed for cytotoxicities against five cancer cell lines; cervical (HeLa), breast cancer (MCF7), lung cancer (A549), stomach cancer (GSU) and Kato III cell lines in vitro. Most of the compounds had slightly inhibitory effects against all or limited tested cell lines. Among them, compound 4q showed moderate cytotoxicity against HeLa, MCF-7, A549, and Kato III cell lines with IC50 values of 28.4 µM, 28.3 µM, 30.7 µM, and 28.5 µM, respectively. The structure-activity relationship analysis suggested that the substructure combination of benzimidazole and naphthalene bearing the free hydroxy group at C-1 and the three methoxy groups at the C-6, C-7, and C-8 of the naphthalene ring may exhibit a synergistic effect and an improved anticancer activity.