A novel synthesis, single crystal and biological activity of 4-acylthiosemicarbazone-3-methyl- 1-(4-methylphenyl)-2-pyrazolin-5-one by condensation of 4-acyl-3-methyl-1-(4- methylphenyl)-2-pyrazolin-5-one with thiosemicarbazide was carried out. The compounds were characterized on the basis of elemental analysis, IR, 1H NMR, Mass, DSC and 13C NMR spectral data. The compounds were tested for their antibacterial activity against ...