The reaction of carboxylic acid derivatives (benzoi c acid‚ 3-(tolic acid‚ 4-tolic acid‚ mefenamic acid ‚ anthranic acid) with (N-isocyanimino)triphenylphosphorane pro ceeds smoothly at room temperature to afford 2-aryl -1,3,4- oxadiazoles via an intramolecular aza-Wittig reacti on in excellent yields under neutral conditions. Th e structures of the products were deduced from their IR, 1 HNMR, and 13 CNMR spectra and mass spectrometry. All the compoun ds have been screened for antibacterial activity again st Escherichia coli ATCC 2921,Pseudomonas aeruginos a ATCC 27853, Staphylococcus aureusATCC 25923, Listeria mo nocytogenes ATCC 23074 and antimycobacterial activi ty against Mycobacterium smegmatis PTCC 1307by the bro th dilution and well agar diffusion methods. The r esults revealed that compounds 5a and 5b have antibacteria l activity against E.coli and compounds 5e and 5d s howed anti-mycobacterial activity.