ln vitro and in vivo antibacterial activities of DWQ-013(1-cyclopropyl-6,8-difluoro-7-(3-methylthiomethylpyrrolidinyl)-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid), a new fluoroquinolone antibacterial agent, were compared with those of ciprofloxacin, sparfloxacin and ofloxacin against aerobic and anaerobic standard strains and clinical isolates. DWQ-013 had a broad spectrum and potent antibacterial activity against Gram-positive and Gram-negative bacteria. The antibacterial activity of DWQ-013 against Staphylococcus aureus was equal to that of sparfloxacin(SPFX) and superior to those of ciprofloxacin(CPFX). The antibacterial activity against Gram-negative bacteria was slightly lower than those of ciprofloxacin and sparfloxacin. MIC of DWQ-013 against Pseudomonas aeruginosa$(0.781{sim}1.563;{mu}g/ml)$ was usually equal to that of sparfloxacin$(0.781;{mu}g/ml)$ and was inferior to that of ciprofloxacin$(0.098;{mu}g/ml)$. The number of viable cells was decreased rapidly after addition of DWQ-013 at concentration of $1{sim}2$ folds of MIC.