Pyrazoleone pyrazoles are prepared by condensing 3-(2-phenylhydrazono)pentane-2,4-dione with hydraz ezene hydrate in presence of suitable condensing agents. They undergo a variety of chemical reactions and ar e found useful in synthesis of variety of biologically acti ve mannich derivatives of heterocyclic compounds. Mannich reaction is one of the versa tile reaction widely used in organic synthesis. This reaction is useful for synthesizing N- methyl derivatives and many drug molecules. Mannich base derivatives of pyrazolone pyrazoles play an i mportant role in medical field with so many pharmaceutical i mportance such as antibacterial, antituberculosis a ntineoplastic, antidiabetic anti fertility and anti hydthyroid act ivity. anthelmintic, antifungal, anti-inflammatory , antiviral and analgesic properties. The potency of these clinical ly useful drugs encouraged the synthetic chemists f or the synthesis of some more potent and significant compounds..