Twenty-four novel 2,5-diaryl-1,3,4-oxadiazoline analogs of combretastatin A-4 (CA-4, 1) were designed, synthesized and evaluated for biological activities. The compounds represent two structural classes; the Type I class has three methoxy groups on the A ring and the Type II class has a single methoxy group on the A ring. Biological evaluations demonstrate that multiple structural features control the biological potency. Four of the compounds, 2-(3'-bromophenyl)-5-(3",4",5"-trimethoxyphenyl)-2-acetyl-2,3-dihydro-1,3,4-oxadiazoline (9l), 2-(2',5'-dimethoxyphenyl)-5-(3"-methoxyphenyl)-2-acetyl-2,3-dihydro-1,3,4-oxadiazoline (10h), 2-(3',4',5'-trimethoxyphenyl)-5-(3"-methoxyphenyl)-2-acetyl-2,3-dihydro-1,3,4-oxadiazoline (10i) and 2-(3',5'-dimethoxyphenyl)-5-(3"-methoxyphenyl)-2-acetyl-2,3-dihydro-1,3,4-oxadiazoline (10j), have potent antiproliferative activities against multiple cancer cell lines. Mechanistic studies indicate that they retain the microtubule disrupting effects of compound 1 including microtubule loss, the formation of aberrant mitotic spindles, and mitotic arrest. Compound 10i inhibits purified tubulin polymerization and circumvents drug resistance mediated by P-glycoprotein and βIII tubulin expression. The oxadiazoline analog 10i is a promising lead candidate worthy of further investigation.