A new series of 5-thiazolyl-ethylidene-hydrazinyl-thiazoles 3a-g, 5-thiazolil-ethylidene-hydrazinyl-thiazolin-4-ones 5 and 6a-i was synthesized starting from 5-acetyl-2-phenyl-4-methyl-thiazolyl-thiosemicarbazone 2 by the reaction with various α-halocarbonyle compounds or ethyl-α-chloroacetate. The 5-thiazolyl-1,3,4-thiadiazoline 4 was synthesized by ciclysation of the same thiosemicarbazone 2 with acetic anhydride in the presence of pyridine. The newly synthesized compounds were characterized by 1 H-NMR and mass spectral studies. Rezumat Prin reacţia tiosemicarbazonei 5-acetil-2-fenil-4-metil-tiazolului 2 cu diverşi α-halocarbonili sau α-cloro-acetat de etil s-au obţinut noi serii de compuşi cu structură 5-tiazolil-etiliden-hidrazinil-tiazolică 3a-g şi 5-tiazolil-etiliden-hidrazinil-tiazolin-onică 5 şi 6a-i. Prin ciclizarea aceleaşi tiosemicarbazone 2 cu anhidridă acetică, în prezenţă de piridină, s-a obţinut compusul 4, cu structură 5-tiazolil-1,3,4-tiadiazolinică. Noii compuşi sintetizaţi au fost caracterizaţi prin 1 HRMN şi studii spectrale de masă.