This invention relates to:rn- PLGA (poly lactic-co-glycolic acid, i.e. a copolymer of poly lactic acid (PLA) and poly glycolic acid) microparticles loaded with a fluoroquinolone with high mucosal permeability,rn- the method of preparation thereof andrn- applications thereof.rnrnThe invention could notably be used in the treatment of pulmonary infections, such as bacterial bronchitis, bronchiolitis and pneumonia. rnrnFluoroquinolones constitute a family of antibacterial agents. Fluoroquinolones are indicated for the treatment of several bacterial infections.rnSeveral bacterial infections include but are not limited to, respiratory infections such as bacterial bronchitis, bronchiolitis, pneumonia, tuberculosis, tonsillitis pharyngitis, otitis and sinusitis, septicaemia, typhoid fever, joint and bone infections, soft tissue and skin infections, gastrointestinal infections and urogenital infections.rnMore particularly, fluoroquinolones are known to have an activity against a wide range of gram-positive and gram-negative organisms.rnrnThe inventors have found and demonstrated that the PLGA microparticles loaded with a fluoroquinolone with high mucosal permeability of the present invention enable to improve the fluoroquinolone efficiency against bacterial agents in comparison to free fluoroquinolones.rnrnThey have also demonstrated that a pulmonary administration of the PLGA microparticles loaded with a fluoroquinolone with high mucosal permeability of the present invention, results in a prolonged release of the fluoroquinolone within the lung and in much higher fluoroquinolone concentrations in pulmonary system, in particular in lung epithelial lining fluid (ELF).rnrnThey have also demonstrated that specific PLGA microparticles loaded with a fluoroquinolone, in term of nature of PLGA, PLGA particle size and fluoroquinolone content enable to reduce the frequency of administrations, to increase anti-infectious treatment efficiency while reducing systemic toxicity. Indeed, the PLGA microparticles loaded with a fluoroquinolone with high mucosal permeability of the present invention have fluoroquinolone sustained-release of at least 72 hours.