There have been a little attempts to draw analogy between architecture and music. There are many objective and subjective factors for this to be true. If, however, the two arts are out of much the same social conditions, they show a degree of conformity in design and general organization. Our study shows the interrelationship between Otto Wagner and Gustav Mahler in Belle Epoque. In order to clarify the interrelationship between architecture and music, this study examines works of Otto Wagner on the basis of the characteristic of Gustav Mahler. This comparison between Otto Wagner and Gustav Mahler follows : in Belle Epoque, they have the same tendency to 1) the disintegration of historicism, 2) the style of description, 3) the reversion, 4) the giganticness, 5) the change of materials and 6) the proportion.