Twenty-six unsymmetrical biphenyls were synthesized and evaluated for cytotoxic activity against DU145, A549, KB and KB-Vin tumor cell lines. Three compounds 27, 35 and 40 showed very potent activity against the HTCL panel with an IC(50) value range of 0.04-3.23 microM. In addition, fourteen active compounds were all more potent against the drug-resistant KB-Vin cell line than the parental KB cell line. Preliminary SAR analysis indicated that two bulky substituents on the 2,2'-positions of unsymmetrical biphenyl skeleton are necessary and crucial for in vitro anticancer activity, thus providing a good starting point to develop unsymmetrical biphenyls as novel anticancer agents.