We have discovered several tubulin-active compounds in our previous studies. In the establishment of a compound library of small molecule weight tubulin ligands, 14 new N-3-haloacylaminophenyl-N'-(alkyl/aryl) urea analogs were designed and synthesized. The structure-activity relationship (SAR) analysis revealed that (i) the order of anticancer potency for the 3-haloacylamino chain was following -CH(2)Br>-CHBrCH(3); (ii) the N'-substituent moiety was not essential for the anticancer activity, and a proper alkyl substitution might enhance the anticancer activity. Among these analogs, the compounds 16j bearing bromoacetyl at the N'-end exhibited a potent activity against eight human tumor cell lines, including CEM (leukemia), Daudi (lymphoma), MCF-7 (breast cancer), Bel-7402 (hepatoma), DU-145 (prostate cancer), DND-1A (melanoma), LOVO (colon cancer) and MIA Paca (pancreatic cancer), with the IC(50) values between 0.38 and 4.07 microM. Interestingly, compound 16j killed cancer cells with a mechanism independent of the tubulin-based mechanism, indicating a significant change of the action mode after the structure modification.