Novel 4-oxoquinoline-3-carboxylic acid compounds of the formula: ##STR1## wherein R.sup.1 is cyclopropyl which may have 1 to 3 substituents of alkyl and halogen; phenyl which may be substituted by 1 to 3 substituents of alkoxy, halogen and OH; alkyl which may be substituted by halogen, alkanoyloxy or OH; alkenyl; or thienyl, R.sup.2 is 5- to 9-membered saturated or unsaturated heterocyclic ring which may be sustituted, R.sup.3 is alkyl or halogen, R.sup.4 is alkyl or halogen, R is H or alkyl, R.sup.1 and R.sup.3 may be taken together to form ##STR2## wherein R.sup.31 is H or alkyl, and X is halogen, provided that R.sup.3 and R.sup.4 are not simultaneously halogen, and salts thereof, said compounds having excellent antimicrobial activity and hence being useful as an antimicrobial agent, and a pharmaceutical composition containing said compound as an active ingredient.