The present invention provides a method of preparing a planographic printing plate comprising the steps of:(1) exposing a DTR mono-sheet material containing a silver halide emulsion layer and a nuclei containing surface layer in a laser beam containing device, e.g. a helium-neon laser, an argon laser, or a semiconductor laser, wherein the said emulsion layer contains at least one emulsion showing following characteristics:(a) the emulsion consists principally of silver chloride but contains bromide ranging from 5 mole % to 40 mole % and iodide ranging from 0 to 1 mole %;(b) the emulsion belongs to the core-shell type wherein substantially all the bromide is concentrated in the core;(c) the emulsion grains contain Rhodium and/or Iridium dopants;(2) processing the DTR material by means of a developing or activator solution, containing at least an alkali agent and a silver halide complexing agent, followed by a neutralization solution.