Synthesis of the carbothioamides (5, 13, 22) was performed starting from 3H-1,2,4-triazol-3-ones (2, 17) by several steps, and then, these carbothioamides was converted to triheterocyclic compounds incorporating 1,2,4-triazole, imidazole and 1,3-thiazol(idinone) moieties. The reaction of compound 2 with 3,4-difluoronitrobenzene afforded the 2-(2-fluoro-4-nitrophenyl) derivative, 10. Compound 10 was converted to the arylideneamino derivatives (12a, b) via the reduction of nitro group. On the other hand, the treatment of the hydrazide (20) that was obtained starting from 17, with several aromatic aldehydes generated the corresponding arylidenhydrazides (21a–c). Mannich reaction between compound 2 and a suitable heterocyclic amine resulted in the N-alkylation of 2. All newly synthesized compounds were screened for their antimicrobial activities. In general, most compounds except 22 were Found (%) to be active against Mycobacterium smegmatis, Candida albicans and/or Saccharomyces cerevisiae. Furthermore, 9a and b, which are Mannich bases incorporating morpholine or piperazine nucleus, exhibited excellent antimicrobial activity on test microorganisms. In addition, the hydrazide, 4, was Found (%) to have activity towards Ec and Yp.