Mannich bases of ethyl 5-(2-chlorophenyl)-7-methyl-3-oxo-3,5-dihydro-2H-thiazolo[3,2-a]pyrimidine-6-carboxylate (6) were prepared by Mannich reaction respectively with seven different heterocyclic secondary amino compounds (8a-g) and formaldehyde (7). Compound (6) were derived by the cyclization reaction of ethyl 4-(2-chlorophenyl)-6- methyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate (4) with chloroacetic acid (5) in dimethylformamide (DMF). The precursor compound (4) was prepared by a Biginelli reaction of 2-chlorobenzaldehyde (1) with ethylacetoacetate (2) and thiourea (3). All the newly synthesized Mannich bases were analyzed with a view to elucidate their chemical structure by elemental analysis and spectral studies (FTIR, 1H & 13C NMR). They were assayed in vitro for their biological activity against Escherichia coli and Bacillus subtilis bacterial species as well as Aspergillus niger and Candida albicans fungal microorganisms. Evaluation of the title compounds as antimicrobacterial agent indicate that ethyl-5-(2-chlorophenyl)-7-methyl-2-(morpholinomethyl)-3-oxo-3,5-dihydro- 2H-thiazolo [3,2-a]pyrimidine-6-carboxylate (9e) have shown promising antimicrobacterial activity against both bacterial and fungal microorganisms and thus could be promising novel drug candidates.