ABSTRACT.A series of eight new quinoline associated 1,3,4-thiadiazolo pyrimidin derivatives (5a-h) have been developed using 4-amino-8-fluoro-quinoline-3-carboxylic acid ethyl ester (1) as raw material and by involving 8-fluoro-4-methylsulfanylthiocarbonylamino-quinoline-3-carboxylic acid ethyl ester (2), 8-fluoro-4-hydrazine thiocarbonylamino-quinoline-3-carboxylic acid ethyl ester (3) and 3-amino-7-fluoro-2-mercapto-3H-pyrimido-[5,4-c]quinolin-4-one (4) as intermediates. The title compounds after structure elucidation were used in vitro to find their antibacterial ability towards different micro-organisms.