In the present study, 1-acetyl-3-(2-thienyl)-5-aryl-2-pyrazoline derivatives (1-6) were synthesized via the ring closure reaction of 1-(2-thienyl)-3-aryl-2-propen-1-ones with hydrazine hydrate in acetic acid. The chemical structures of the compounds were elucidated by IR, H-1-NMR, C-13-NMR and mass spectral data and elemental analyses. MTT assay, analysis of DNA synthesis and caspase-3 activation assay were carried out to determine anticancer effects of the compounds on A549 and C6 cancer cell lines. They exhibited dose-dependent anticancer activity against A549 and C6 cancer cell lines. Anticancer activity screening results revealed that compounds 1, 2 and 4 were the most potent derivatives among these compounds. But anticancer effects of these compounds may result from different death mechanisms in A549 and C6 cell lines.