The present invention provides a method for treating a substrate that supports metal fine particles for forming a plating layer on a circuit pattern or TSVs in various substrates, in which further micronization treatment is enabled compared with the conventional methods, and the formation of a stable plating layer is enabled. The present invention is a method for treating a substrate, the method including bringing a substrate into contact with a colloidal solution containing metal particles in order to support the metal particles that serve as a catalyst for forming a plating layer on the substrate, in which the colloidal solution contains metal particles formed of Pd and having a particle size of 0.6 nm to 4.0 nm and a face-to-face dimension of the (111) plane of 2.254 Å or more. When an organic layer such as SAM is formed on a surface of the substrate before this treatment, the binding force of the Pd particles can be increased.