In our present study 4-substitutedaniline (1a) has been reacted with acetyl acetone (1b) in presence of sodium nitrite and sodium acetate yielded 3-[2-(4-substitutedphenyl)-hydrazono]-pentane-2, 4-dione (2a-b). Compound (2a-b) react with hydrazine hydrate and phenyl hydrazine to give 4-[(4-substitutedphenyl)-diazenyl]-3, 5-dimethyl-1Hpyrazole (3a-b) and 4-[(4-substitutedphenyl)-diazenyl]-3, 5-dimethyl-1-phenyl-1H-pyrazole (4a-b) respectively. 1- [4-((4-substitutedphenyl)-diazenyl)-3, 5-dimethyl-1H-pyrazol-1-yl]-ethanone (5a-b) has been synthesized by the treatment of 4-[(4-substitutedphenyl)-diazenyl]-3, 5-dimethyl-1H-pyrazole (3a-b) with acetyl chloride in pyridine. All the synthesized compounds were characterized on the basis of melting point, IR spectra and NMR spectra.