The intermediate Benzimidazo[1,2-c] quinazolin-6(5H)-thione (1) was obtained by cyclization of 2-(2'-aminophenyl) benzimidazole with carbon disulfide. Mannich base (2a-d) of compound (1) was obtained on treatment with Para formaldehyde and secondary aliphatic amines, similarly treatment of (1) with different ketones afforded respective mannich bases (3 e-h). All derivatives synthesized were characterized from IR and 1HNMR spectral data's. Moderate anti bacterial activity was exhibited from 2a-d and from 3f, 3h against S. aureus, E. coli, and E. fecalis but very negligent activity were seen from these compounds when screened against P aeruginosa.