Purpose: Delivery of ciprofloxacin to alveolar macrophages arid antibacterial effect against intracellular parasites following pulmonary administration of ciprofloxacin incorporated into liposomes were investigated in rats.Methods: Unmodified and mannosylated CPFX-liposomes.(particle sizes: 100-2000 nm) were prepared by hydration method.These CPFX-liposomes (200 μg CPFX/kg) were administered to the lungs of rats.The concentrations of CPFX in plasma and alveolar macrophages (AMs) were determined by HPLC analysis after administration.The antibacterial and mutant prevention effects in AMs were predicted.Results: The delivery efficiency of CPFX to AMs following administration of unmodified CPFX-liposomes increased with the increase in the particle size over the range 100-1000 nm and became constant at over 1000 nm.The delivery efficiency of CPFX to AMs following pulmonary administration of.mannosylated CPFX-liposomes at a particle size of 1000 nm was significantly higher than that of unmodified CPFX-liposomes at a same size.The concentration of CPFX in AMs following administration of mannosylated CPFX-liposomes was markedly higher than that of CPFX solution.On the other hand, the concentration of CPFX in plasma following administration of mannosylated CPFX-liposomes was tended to be lower than that of CPFX solution.Conclusion: The present study has shown that mannosylated CPFX-liposomes as pulmonary administration systems are useful for treatment of respiratory intracellular parasite infections.