Design of a new series of 1,3,4‐oxadiazole derivatives was achieved in good yield via treatment of N‐arylidene‐2‐(1‐oxo‐4‐(4‐phenoxyphenyl)phthalazin‐2(1H)‐yl)acetohydrazide with cerium (IV) ammonium nitrate as a catalyst. They can be formulated also using one‐pot reaction of 2‐(1‐oxo‐4‐(4‐phenoxyphenyl)phthalazin‐2(1H)‐yl)acetohydrazide, aromatic aldehyde and cerium (IV) ammonium nitrate in dichloromethane. The structural formulas of all synthesized products were elucidated based on their elemental and spectral analyses. In addition, MTT assay was used to evaluate antitumor activity of the synthesized molecules and some of them showed potent activity in comparison with Doxorubicin as a standard drug.