Quinolylpropylpiperidine derivatives of general formula (I) in which R1a is hydrogen, halogen, hydroxyl, amino, alkylamino, dialkylamino, hydroxyamino, alkoxyamino or alkylalkoxyamino and R1b is hydrogen, or R1a and R1b form an oxo, R2 is carboxyl, carboxymethyl or hydroxymethyl, R3 is alkyl either substituted with phenylthio optionally substituted with halogen, hydroxyl, alkyl, alkoxy, trifluoromethyl, trifluoromethoxy, carboxyl, alkoxycarbonyl, cyano or amino, or with cycloalkylthio (3 to 7 members) optionally substituted with halogen or trifluoromethyl, or with heteroarylthio (5 to 6 members and 1 to 4 heteroatoms chosen from N, O and S), optionally substituted with halogen, hydroxyl, alkyl, alkoxy, trifluoromethyl, trifluoromethoxy, carboxyl, alkoxycarbonyl, cyano or amino or R3 is propargyl substituted with phenyl or heteroaryl as defined above, R4 is alkyl, alkenyl-CH2— or alkynyl-CH2—, cycloalkyl or cycloalkylalkyl, in their various isomeric forms, separate or as mixtures, and also their salts, their preparation process and intermediates and the compositions containing them. These novel derivatives are potent antibacterial agents.