New series of 2-substituted aryl amine, heteryl amine and active methylene group compound derivatives of 9-chloro- 3-cyano-8-fluoro-2-methylthio-4-oxo-4H-pyrimido [2, 1-b] [1, 3] benzothiazole are synthesized. The antimicrobial activity of the synthesized compounds were studied by disc diffusion method using various strains of microbes and compared with the standard drug streptomycin. The antifungal activity was also evaluated against four fungal strains and compared with Amphotericin-B as standard. The biological activity of the synthesized compounds was found to be good to moderate .