Two series of novel quinoline derivatives; oxadiazolyl and thiadiazolyl quinolines were prepared and evaluated for their antimicrobial activities. The first series; 5-(2-aryl-6-substituted-4-quinolyl)-1.3,4-oxadiazol-2-amines (V_a-g) was synthesized by cyclization of the key intermediate thiosemicarbazides (IV_1-7). The second one; 5-(2-aryl-6-substituted-4-quinoly!)-1,3.4- thiadiazol-2-amines (VI _a.c.f.g) was synthesized through cyclization of the key intermediate quinoline-4-carboxylic acids (_I1-7) or from the synthetically accessible thiosemicarbazides (IV_1-7).The target oxadiazole and thiadiazole derivatives were evaluated against Gram positive, Gram negative bacteria and fungi. The obtained results showed that the 1,3,4-thiadiazoles VI _4,8 exhibited the most potent antibacterial activity with MIC values of 4 µg/ml.