Provided is a coating liquid for forming an undercoat layer of an electrophotographic photoreceptor exhibiting high stability. In the coating liquid for forming an undercoat layer of an electrophotographic photoreceptor containing metal oxide particles and a binder resin, the metal oxide particles have a cumulative volume average diameter D50 of 0.1 μm or less and a volume particle size distribution width index SD satisfying the following Expression (1) which are measured by a dynamic light-scattering method in the coating liquid for forming an undercoat layer, 0.010≦SD≦0.040  (1) where SD=(D84−D16)/2, where D84 represents the particle diameter (μm) at a point of 84% in the cumulative volume particle size distribution curve, and D16 represents the particle diameter (μm) at a point of 16% in the cumulative volume particle size distribution curve.