A novel method was performed for optical fabrication of nano-structures on organic photosensitive thin films utilizing evanescent waves on prism surface. The evanescent waves are produced by means of total internal reflection of laser beams on a prism surface and the intensity shows exponential decay from the surface. Nano-patterns of surface relief gratings (SRGs) were inscribed for spin-coated azo dye (congo red) films showing photoisomerization by the evanescent waves. The cycle pattern of the SRG was approximately 210nm that was smaller than a half of the incident laser wavelength of 488 run. In the conventional technique of fabrication of SRGs, it is very difficult to obtain narrower lattices and one can not obtain any smaller lattices of SRGs than a half wavelength of the laser beam. This techniques based on molecular migration due to evanescent waves are thought to be very useful for nano-device processing and future device applications.