Novel imidazoquinolone derivative represented by the formula (I);
wherein R 1 represents hydrogen, alkyl, cycloalkyl, alkenyl aralkyl, aralkenyl or substituted or unsubstituted aryl; X represents nitrogen or C-R 2 where R 2 is hydrogen, hydroxyl, alkyl, cycloalkyl, alkenyl, aralkyl, aralkenyl, substituted or unsubstituted aryl, thiol, halogen, substituted or unsubstituted aromatic heterocyclic group, or -(CH 2 ) m C0 2 R 6 where R 6 is hydrogen or lower alkyl and m is an integer of 0 to 3; Y represents oxygen or sulfur; R 3 represents alkyl, cycloalkyl, alkoxyalkly, alkenyl, aralkyl; aralkenyl, -(CH 2 ) n -Het where Net is substituted or unsubstituted aromatic heterocyclic group and n is an integer of 1 to 3 or (CH 2 )- n CO 2 R 6a where n has the same meaning as defined above and R 6a has the same meaning as defined as to R 6 ; each of R 4 and R 5 independently represents hydrogen, lower alkyl, trifluoromethyl, cycloalkyl, halogen, hydroxyl, lower alkoxyl, lower alkylthio, nitro, amino, lower alkylamino, lower alkanoylamino, aroylamino, lower alkanoyl or aroyl; and a pharmaceutically acceptable salt thereof. The Compound (I) and a pharmaceutically acceptable salt thereof show bronchodilatory and antiallergic activities, and are useful for treating respiratory disorders such as bronchial asthma.