Abstract: Provided is an electroless plating method for a low temperature co-fired glass ceramic substrate, the method including: a degreasing and activation treatment step of degreasing and activating a surface of a wiring pattern formed of a silver sintered body; a catalyzing step of providing a catalyst onto the surface of the wiring pattern formed of a silver sintered body; and an electroless multi-layered coating plating treatment step. The electroless plating method further includes, between the degreasing and activation treatment step and the catalyzing step, a silver precipitation treatment step of precipitating silver on a glass component present on the surface of the wiring pattern formed of a silver sintered body after the degreasing and activation treatment step, and the catalyzing step includes providing the catalyst also to the silver precipitated in the silver precipitation treatment step.