4-Substituted 6-cyclopropyl-6, 9-dihydro-5-methoxy-9-oxo-1H-imidazo[4,5-f] quinoline-8-carboxylic acids (6) and 8-substituted 1,5,6,11-tetrahydro-5-methyl-1-oxo-imidazo[4,5-g]pyrido[1,2,3-de][1,4] benzoxazine-2-carboxylic acids (7) were prepared as potential antibacterial quinolone derivatives. The appendages at C-4 of -6 and at C-8 of -7 were selected from 1-piperazinyl, 4-methylpiperazinyl, 3-aminomethylpyrrolidinyl, and 3-aminomethylpyrrolidinyl groups. The 5-methoxyimidazoquinolones 6 were superior to the corresponding ofloxacin type analogues 7 in in vitro antibacterial activity. The activity of 6 was equipotent against S. aureus, but 2 to 16 times less potent against E. coli and P. aeruginosa compared to that of the 5-fluoro analogue 3.