Abstract: Novel imidazoquinolone derivative represented by the formula (I); ##STR1## wherein R.sup.1 represents hydrogen, alkyl, cycloalkyl, alkenyl aralkyl, aralkenyl or substituted or unsubstituted aryl; X represents nitrogen or ##STR2## where R.sup.2 is hydrogen, hydroxyl, alkyl, cycloalkyl, alkenyl, aralkyl, aralkenyl, substituted or unsubstituted aryl, thiol, halogen, substituted or unsubstituted aromatic heterocyclic group, or --(CH.sub.2).sub.m CO.sub.2 R.sup.6 where R.sup.6 is hydrogen or lower alkyl and m is an integer of 0 to 3; Y represents oxygen or sulfur; R.sup.3 represents alkyl, cycloalkyl, alkoxyalkly, alkenyl, aralkyl, aralkenyl, --(CH.sub.2).sub.n -- Het where Het is substituted or unsubstituted aromatic heterocyclic group and n is an integer of 1 to 3 or --(CH.sub.2).sub.n CO.sub.2 R.sup.6a where n has the same meaning as defined above and R.sup.6a has the same meaning as defined as to R.sup.6 ; each of R.sup.4 and R.sup.