Syntheses of 1,2,4-triazol-3-ones, 4a, 4b, and 5 were performed starting from ester ethoxycarbonylhydrazones (1a, 1b) that were reported earlier. The treatment of triazole derivatives, 4a, 4b, and 5 with several sulfonyl halides produced the corresponding sulfonamides, 6–10. Syntheses of carbo(thio)amides, 15, 17, and 18 were carried out by the treatment of (substituted)phenyliso(thio)cyanates with hydrazides 13, 14 which were obtained starting from 4a and 5 by two steps. Cyclization of compounds 15 and 17 in basic media resulted in the conversion of carbo(thio)amide side chain to 5-oxo- or 5-mercapto-1,2,4-triazole ring. Cyclocondensation of 17 with ethyl chloroacetate and 4-nitrophenacylbromide gave 1,3-thiazolidin, 20 and 1,3-thiazol 21, derivatives, respectively. Newly synthesized compounds were screened for their antimicrobial activities, and some of them displayed activity against the test microorganisms. Then the highest activity was observed for compounds 6 and 7 carrying cyclic sulfonamide function beside 1,2,4-triazole nucleus.