This invention offers isoxazole derivatives represented by the following formula (I) in which R1 and R2 each stands for hydrogen, lower alkyl, amino and the like; R3 stands for substituted or unsubstituted aryl or hetero aryl; R4 stands for hydrogen or lower alkyl; R5 stands for substituted or unsubstituted phenyl, furyl and the like; and Y stands for —CH2—, —CO—, —O—, —NH— and the like, or pharmaceutically acceptable salts thereof which exhibit excellent p38MAPkinase-inhibiting action with reduced side-effects, and are useful for treating such diseases as chronic rheumatoid arthritis, ulcerative colitis and the like.