A series of novel 5-alkyl/aryl thiadiazole substituted thiazolidin-4-ones were synthesized by a two-step process. In the first step, 5-alkyl/aryl substituted 2-aminothiadiazoles were synthesized, which on reaction with substituted aromatic aldehydes and thioglycolic acid in the presence of dicyclohexylcarbodiimide afforded thiazolidin- 4-ones. All the compounds were synthesized in fairly good yields and their structures were confirmed by spectral and physical data. The title compounds were screened for in vitro anti-proliferative activity on human breast adenocarcinoma cells (MCF-7) by MTT assay. Most of the derivatives showed an IC50 less than 150 μmol L-1. Among the compounds tested, 2-(2-nitrophenyl)- 3-(5-methyl-1,3,4-thiadiazol-2-yl)-thiazolidin-4-one (