PURPOSE: To rapidly and firmly form a Pd film on the surface of an electric insulator by chemically plating the insulator with a soln. of a Pd-urea complex salt and a reducing agent and electrodepositing Pd on the insulator from the same plating soln.

CONSTITUTION: An electric insulator such as ceramics is chemically plated with a soln. of a Pd-urea complex salt such as Pd(NH2CONH2)Cl2 and a reducing agent for the salt such as sodium borohydride. Pd is then electrodeposited on the insulator by supplying electric current to the same plating soln. with the cathode brought into contact with an electrically conductive film formed by the chemical plating and the anode brought into contact with the plating soln. A Pd film is rapidly and firmly formed on the surface of the electric insulator.