Abstract: Carbostyril derivatives having antihistamic action and central nervous controlling action are useful as antihistamic agents or central nervous controlling agents. The derivatives are represented by the general formula, ##STR1## wherein R.sup.1 is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, an alkynyl group having 2 to 4 carbon atoms or a phenylalkyl group having an alkylene group containing 1 to 4 carbon atoms; R.sup.2 is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a phenyl group; R.sup.3 is a hydrogen atom, a hydroxy group, an alkyl group having 1 to 4 carbon atoms, an alkanolyoxy group having 1 to 4 carbon atoms or a 3,4,5-trimethoxybenzoyloxy group; R.sup.4 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R.sup.