A substrate processing method includes (A) supplying to the substrate a first processing liquid containing a removing agent for deposit, a solvent having a boiling point lower than that of the removing agent and a thickener, (B), after (A), supplying to the substrate a second processing liquid containing an organic polymer to be a gas diffusion barrier film, (C), after (B), heating the substrate at a predetermined temperature equal to or higher than the boiling point of the solvent and lower than the boiling point of the removing agent to promote evaporation of the solvent and reaction between the deposit and the removing agent, and (D), after (C), supplying a rinsing liquid to the substrate to remove the deposit from the substrate. The gas diffusion barrier film prevents a gaseous reactive product generated by the reaction in (C) from diffusing around the substrate.