Pyridazine and pyridazinone derivatives compounds are biologically important compounds. Pyridazinone has carbonyl group on third carbon on pyridazine ring. Pyridazine and pyridazinone is a wonder nucleus because their derivatives give amost all types of biological activities such as such as analgesic, antiinflammatory, antimicrobial, antisecretory, antiulcer, antidepressants, neuroleptics, anxiolytics, sedative, hypnotic, tranquillizer, anticonvulsant, antiplatelet, antithrombotics, anticancer, antihistamine, cardiotonics, vasodilatators, antiarrhythmics, antidiabetic, antihypertensive, antitubercular and various other types of activities. These compounds are synthesized with the aim of novel agents those possess interesting biological activities. The present review has been focused on the pyridazine and pyridazinone derivatives with potential pharmacologica activities.