This invention provides a method for forming a multilayer coating film, comprising applying a base paint (X) having a solids content ratio of 30 to 62 mass % to a substrate to form a base coating film having a cured film thickness of 6 to 45 μm; applying an effect pigment dispersion (Y) having a solids content ratio of 0.1 to 10 mass % to the base coating film to form an effect coating film having a cured film thickness of 0.1 to 5.0 μm; applying a two-component clear paint (Z) containing a hydroxy-containing resin and a polyisocyanate compound to the effect coating film to form a clear coating film; and heating the base coating film, the effect coating film, and the clear coating film to simultaneously cure these coating films; wherein the base paint (X) contains a polyurethane resin (A), an alcohol (B) containing 6 to 12 carbon atoms, and an organic solvent (C) having an HLB of 7 to 9, and the effect pigment dispersion (Y) contains water, a flake-effect pigment (P), a resin emulsion (Q), and cellulose nanofibers (R).