In a process for electroless copper plating in an electroless copper plating solution containing a copper salt, a complexing agent for the copper salt, a reducing agent for the copper salt, and a pH-adjusting agent, a plating film having distinguished mechanical properties can be obtained by adding at least one of soluble inorganic silicon compounds and soluble inorganic germanium compounds and conducting the electroless copper plating by injecting an oxygen-containing gas into the plating solution or by adding an oxidizing agent to the plating solution or by both injection or the oxygen-containing gas and addition of the oxidizing agent thereto. The stability of the electroless copper plating solution can be maintained better thereby and substantially thick plating is possible.