In this study, seven new 3(2H)-pyridazinone derivatives expected to show cytotoxic activity in liver and colon cancer cell lines were synthesized. Their structures were confirmed by the IR, H-1-NMR, C-13-NMR spectra and elementary analyses. Compunds V-1-V-7 were tested on HEP3B (liver cancer) and HTC116 (colon cancer) cell lines for cytotoxicity by using MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] proliferation assay. Human fibroblast cells were used as safety control in these tests. 6-[4-(2-Fluorophenyl)piperazine-1-yl]-3(2H)-pyridazinone-2-acetyl-2-(2-chlorobenzal) hydrazone (compound V-3) was the most active agent with respect to HEP3B and HTC116 cell lines.