A photothermographic material having, on at least one side of a support, an image forming layer containing at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent, and a binder, and an X-ray image forming method using the same, wherein 50% or more of a total projected area of the photosensitive silver halide is occupied by tabular grains having an aspect ratio of 2 or more, and the grains have at least one epitaxial junction portion having a multifold structure. A photothermographic material with high sensitivity and excellent storage stability, and an image forming method using the material are provided.