A series of 5-substituted 2-(p-methoxyphenyl)-1H-benzimidazoles was synthesized and evaluated for cytotoxicity against 4 human cancer cell lines, HCT 15, PC-3, A549, and ACHN. Except for the 5-chloro analogue, most of the 5-substituted compounds showed significant cytotoxicities in these cell lines. However, the structure activity relationship study revealed that neither the electronic nor the lipophilic parameters of the 5-substituents were related to cytotoxicity. Moreover, none of the analogues showed significant NF к-β inhibition activity implying that cytotoxicity was not related to this mechanism. The 5-methyl analogue was the most potent compound in this series with a GI50 of 0.9 µM in the A549 cell line.