In this study, 12 new 3(2H)-pyridazinone derivatives carrying 4-substituted phenylpiperazinylethyl moiety on lactam nitrogen were synthesized and their chemical structures were confirmed by 1 H-NMR, mass, and elemental analysis. Analgesic and anti-inflammatory activities of the synthesized compounds were evaluated in mice. Among the synthesized compounds, compound 9c showed the best analgesic and anti-inflammatory activities without causing any gastric effect in stomachs of tested animals. In addition, the synthesized compounds were screened for their antibacterial and antifungal activities against some pathogenic strains.