Holograms were formed on a silver halide photothermographic material without carrying out wet treatment. Amplitude holograms whose gratings consist of rows of developed silver grains were formed, and the maximum diffraction efficiency of the gratings was almost 1.5%. When the amplitude holograms were bleached using bromine gas, they were converted to phase holograms, and the diffraction efficiency increased to a maximum of 6%. All areas turned yellow in color because of the formation of silver bromide. The mechanism of formation of gratings after bleaching has not yet been established. The authors propose that stripes of silver bromide, developer, toner, or other components may be formed by thermal development and subsequent bleaching. These stripes are transparent but have different diffraction indices, and this leads to the formation of gratings.