The reaction of 6-amino-5-formyl (or acetyl) uracils (4) possessing a phenyl group at the 1-position with caustic alkali resulted in Dimroth rearrangement to give 6-anilino-5-formyl (or acetyl) uracils (5). This is the first example of Dimroth rearrangement observed in the uracil ring system. The presence of both the N1-phenyl group and the 5-formyl (or acetyl) group on the uracil ring is requisite for the occurrence of the rearrangement.