Acetic acid ethyl esters containing 5-oxo-[1,2,4]triazole ring (2) were synthesized by the condensation of compounds 1a-f with ethyl bromoacetate in basic media. The reaction of compounds 2a-f with hydrazine hydrate led to the formation of acid hydrazides (3a-f). The treatment of compounds 3 with two divers aromatic aldehydes resulted in the formation of arylidene hydrazides as cis-tralls conformers (4a,c,e,f, 5a,e,f). The thiosemicarbazide derivatives (6a,c,d,f) were afforded by the reaction of corresponding compounds 3 with phenylisothiocyanate. The treatment of compounds 6a,c,d,f with sulfuric acidic caused the conversion of side-chain of compounds 6a,c,d,f into 1,3,4-thiadiazol ring; thus, compounds 7a,c,d,f were obtained. On the other hand, the cyclization of compounds 6a,c,d,f in the presence of 2 N NaOH resulted in the formation of compounds 8a,c,d,f containing two [1,2,4]triazole rings which are linked to each other via it methylene bridge. Compounds 4a, f, 5a, 7a, d, f, 8a and d have shown antimicrobial activity against one or more microorganism, but no antifungal activity has been observed against yeast like fungi. Also inhibitory effect on mycelial growth by compounds 4e, 7d and 8f hits been observed. Compounds 4c and 5f were found to possess antitumor active towards breast cancer. (C) 2004 Elsevier SAS. All rights reserved.