A new series of bispyrazolones were obtained upon treating the bishydrazone derivative 1 with dimethylsulphate, acetic anhydride, benzenesulphonyl chloride, piperidine, morpholine, N-methylaniline and formaldehyde respectively. A Mannich base was prepared from the interaction of 4-phenylhydrazone-3-methyl-2-pyrazolin-5-one and n-butylamine. The condensation of an N-hydroxy methyl derivative with ethyl acetoacetate and diethyl malonate led to the formation of the corresponding N-methyl derivatives. Some of the new bispyrazolones were screened to test their antimicrobial potentialities against Fusarium oxysporum fsp. hycopersici.