A quinoline derivative of the formula (I): ##STR1## wherein each phenyl ring of A, B and C can have one or more substituents, X is ##STR2## (R.sup.1 is a hydrogen atom or a lower alkyl group) or ##STR3## (R.sup.2 is a lower alkyl group or a lower alkoxy group), and n is 0 or 1, or its salt, which possesses an inhibitory action against acyl-CoA: cholesterol acyltransferase.