Treatment of 1- aroyl - 4- substituted thiosemicarbazides with concentrated sılphuric acid quickly leads to cyclization to stable 5- [p-{benzoylamino) phenyl] -2 - substituted amino-1,3,4- thiadiazoles in high yields at ambient temparature. The structures and purity of these compounds were confirmed using spectrometric and spectroscopic techniques ie UV, IR, MASS, together with their melting point and elemental analyses. Keywords :