To provide a plate making method for a planographic printing plate in which staining property in printing, particularly uncontrolled stain and printing resistance can be ensured without impairing image forming property, a developing-solution- insoluble compound can be dissolved or can be stabilized in a dispersed state for a long time and processing stability can also be improved and to provide a developing solution for a photosensitive planographic printing plate.

In a processing method for a photopolymerizable photosensitive planographic printing plate, the planographic printing plate having a photopolymerizable photosensitive layer is processed with a developing solution containing an alkali silicate and the ethylene oxide and/or propylene oxide adduct of a long chain alcohol and having pH 12.0-12.8 and 3-40 mS/cm electric conductivity after it is imagewise exposed with laser light. In the developing solution for a photopolymerizable photosensitive planographic printing plate containing an alkali silicate and a surfactant and having pH 12.0-12.8 and 3-40 mS/cm electric conductivity, (a) the molar ratio of SiO2 to M2O (M is an alkali metal or ammonium) is 0.75-4.0 and (b) the surfactant is the ethylene oxide and/or propylene oxide adduct of a long chain alcohol.