A radiation image conversion panel exhibiting superior homogeneity of an activator in a phosphor layer and enhanced luminance and sharpness, and a preparation method of the same. Described is the radiation image conversion panel having a stimulable phosphor layer on a support. The stimulable phosphor layer is formed by a vapor-phase growth process so as to have a layer thickness of 50 .mu.m to 1 mm after a thermoplastic resin film is prepared on the support or the stimulable phosphor layer mentioned above is formed on a support composed of a thermoplastic resin containing a carbon fiber.