SUNIL KUMAR*, S. K. SHARMA, SANDEEP JAIN, NEELAM JAIN 1, 3, 4-Thiadiazole, Schiffs base, antibacterial, minimum inhibitory concentration (MIC). 1383-1391 Volume 4, Issue 6 November - December 2013 A series of Schiffs bases i.e., N-(p-substituted benzylidene)-5-propyl-1, 3, 4-thiadiazole-2-amines were synthesized from 2-amino-5-propyl-1, 3, 4-thiadiazole 1 and evaluated for their in vitro antibacterial activity. Reaction of thiosemicarbazide with butanoic acid in presence of concentrated sulfuric acid furnished the compound 1 which on further reaction with different p-substituted benzaldehydes yielded the Schiffs bases 2. These compounds were characterized by spectral analysis. All the synthesized compounds were screened for their in vitro for their antibacterial activity against two Gram positive bacterial strains (Bacillus subtilis and Staphylococcus aureus) and two Gram negative bacterial strains (Escherichia coli and Pseudomonas aeruginosa) and their minimum inhibitory concentration (MIC) were determined.