Synthesis of 6-Methyl-2, 4-dihydro-3H-pyrazol-3-one-4-(4-substituted) Benzylpiperazine derivatives IVP a-e was carried out by bromination of Ethyl aceto acetate (I) with KBr.The reaction was carried out in the presence of Hydrochloric acid and tolune to produce Bromoethyl aceto acetate (II), it is further condensed with substituted Benzylpiperazines in presence of ethanol to obtain condensed compound (III).This upon cyclization with excess of hydrazine hydrate will produce title compounds.All the title compounds IVP a-e were screened for possible antibacterial activity against P. Vulgaris, S. Aureas, E. Coli, B. Subtillus and antifungal activity against Altenaria, Culvalaria, C. Albicans and A. Niger.Among the compounds synthesized IVPb and IVPc demonstrated good antibacterial activity, IVb, IVc, and IVe showed good antifungal activity.The activities of the synthesized compounds are compared with the standard and other test compounds.The structures of synthesized compounds were established by elemental analysis, IR, H NMR and Mass spectral data.