To provide a preparing method of phosphor layer coating liquid capable of manufacturing a radiological image conversion panel having a good face shape and an excellent structural mottle, and a manufacturing method of the radiological image conversion panel.

In this preparing method of phosphor layer coating liquid, a phosphor is added, stirring a solution simultaneously, to the solution prepared by dissolving a bonding agent in a solvent, to disperse the phosphor in the solution. In this case, the phosphor is added slowly, and the phosphor is added, dividedly into plural times. In this manufacturing method of a radiological image conversion panel, a phosphor layer comprising the phosphor layer coating liquid obtained by the preparing method is formed on the surface of a support.