The invention relates to quinolone derivatives with antimicrobial activity and to a process for preparing the same. The claimed quinolone derivatives have a formula wherein Ris 3-methyl-piperidinyl, 4-methyl-piperidinyl, piperidinyl, pyrrolidinyl or morpholinyl and Ris a hydrogen or a chlorine atom. The claimed process consists in the nucleophilic substitution of the hydrogen in the 8th position of the quinolone derivative wherein Ris 3-methyl-piperidinyl, 4-methyl-piperidinyl, piperidinyl, pyrrolidinyl, and Ris a hydrogen atom, while using sulphuryl chloride as chlorination agent in chloroform medium at the room temperature and at a quinolone derivative:sulphuryl chloride molar ratio of 1:3.
