Abstract A series of 3-substituted phenyl -6-substituted phenyl (1,2,4) triazolo (4,3-b) pyridazine has been synthesized. An appropriate aromatic hydrocarbon reacts with succinic anhydride in presence of AlCl3 to yield β-aroyl propionic acid. The corresponding acid was cyclised with hydrazine hydrate to give 6-(substituted aryl)-2, 3, 4, 5-tetrahydro-3-pyridazinone, which was heated on steam bath with phosphorous oxy chloride to yield 3-chloro 6-substituted phenyl pyradazine. This intermediate after reaction with hydrazine hydrate was converted into 3-hydrazino-6-substituted phenyl pyradazine. The resulting product was converted into3-substituted phenyl 6-substituted phenyl (1,2,4) triazolo (4,3-b) pyridazine by reacting with substituted aroyl chloride. Spectral data (IR, NMR, mass spectra) confirmed the structures of the synthesized compounds. The synthesized compounds were investigated for their antiviral activity. The results indicated that the synthesized compounds have mild to potent activity with reference to their appropriate reference standards.