this invention provides a laser marking method that can form a very minute mark of a predetermined shape , such as a letter or pattern , with clarity and high solidity , on the surface of a substrate . the laser marking method of the invention comprises the steps of depositing a coloring material on the surface of a substrate of thermoplastic material to form a thin film of the coloring material , and applying a laser beam to the thin film of the coloring material in conformity with a predetermined marking shape to cause the portions of the substrate irradiated with the laser beam to soften and to cause the thus softened portions to mix with the coloring material , thereby developing the predetermined marking shape on the surface of the substrate .