The present invention relates to a crystalline polymorphic form of 6-fluoro-1-methyl-7- {4-[(5-methyl-2-oxo-1,3-dioxol-4-yl)methyl]piperazin-1-yl}-4-oxo-4H-[1,3]-thiazeto-[3,2- a]-quinoline-3-carboxylic acid (prulifloxacin). More specifically, the invention relates to a crystalline form of prulifloxacin (herein referred to as Form A), and a method for preparing the crystalline Form A. The present invention further provides a pharmaceutical formulation comprising the novel form of prulifloxacin.
