In the present work 2H-Pyrimido[2,1-b]benzothiazole-2-ones were synthesized by reacting 2-aminobenzothiazoles with alkynoic acid in butanol and 4H-Pyrimido[2,1-b]benzothiazole-4-ones were synthesized by the reaction of 2- aminobenzothiazoles with ethylacetoacetate in presence of polyphosphoric acid. The structures of synthesized compound were confirmed by IR, H1NMR & mass spectrum analysis. Synthesized compounds shown biological activity against E. coli and B. Subtilis and anti-fungal activity against A. fumigates.