PURPOSE: To permit printing free of ground staining by one-time passage of processor as well as to obtain quick and complete desensitizing effect with good compatibility with lithographic printing plate by adding a water-swelling inorganic compound fine particles to a desensitizing treatment liquid.

CONSTITUTION: A water-swelling inorganic compound, selected from natural ores (e.g., smectite group of montmorillonite, etc., vermiculite, etc.), and water- swelling synthetic fluoro-mica group including inorganic compounds, wherein OH groups of crystals are partly substituted with fluorine, water-swelling synthetic fluoro-vermiculite group, water-swelling synthetic fluoro-smectite group, etc., where the water-swelling synthetic fluoro-mica group is particularly recommendable, having an average grain size of 1μm or less on dry basis, is added to a desensitizing treatment liquid in a range of 0.5W50g/l preferably. The treatment liquid may contain various desensitizing components or additives, such as inorganic or organic acids or their salts, basic compounds, metal salts, chelating agents, wetting agents, etc. By using the desensitizing treatment liquid, printing free of ground staining can be obtained.