PURPOSE: To provide a new quinolinecarboxylic acid derivative useful for improving an infections disease caused by a Gram-positive bacterium including a methicillin-resistant Staphylococcus and a new quinolone-resistant and methicillin-resistant Staphylococcus.

CONSTITUTION: The derivative of formula I [Z is a (substituted) aromatic hetero group; R1 is H, an alkyl or a (substituted) phenyl; R2 is H, an alkyl, a halogen, etc.; R3 is H or an alkyl; R4 is H, an alkyl, hydroxy, etc.] and its pharmaceutically permissible salt, e.g. 6-fluoro-7-(4-pyridyl)-4-oxo-4H-[1,3]thiazeto[3,2- a]quinoline-3-carboxylic acid. The compound of formula I is obtained, e.g. by a cyclization reaction between a compound of formula II [R8 is an alkyl; Z0 is a (substituted) aromatic heterocyclic group] and a compound of formula III (D and E are each a halogen) in the presence of a deacidification agent (e.g. sodium carbonate) in an inert solvent at 0 to 120°C and, as necessary, a subsequent hydrolysis reaction.