In this study, the azo groups of 2-aryl/alkylamino 5*[p-(1’-phenyl-3’,5’-dimethyl-4’pyrazolylazo)-phenyl]-1,3,4-thiadiazoles which were previously prepared by us were reduced with hydrazine hydrate without a catalyst in ethanol and the following compounds were obtained: 2-n-propylamino-5[p-aminophenyl]-1,3,4-thiadiazole (I), 2-n-buthylamino-5[p-aminophenyl]-1,3,4-thiadiazole (II), 2-cyclohexylamino-5[p-aminophenyl]-1,3,4-thiadiazole (III), 2-phenetylamino-5[p-aminophenyl]-1,3,4-thiadiazole (IV), 2-phenylamino-5[p-aminophenyl]-1,3,4-thiadiazole (V). The structures of these substances were elucidated using UV, IR and NMR spectral methods besides elementary analysis. Keywords :