PURPOSE: To obtain alkaline peeling liquid capable of removing photosensitive resin unnecessitated after solder plating in the preparing process of an IC substrate and capable of preventing the dissolving of solder by incorporating an oxidizing agent in case of mixing alkali liquid to solder plating liquid.

CONSTITUTION: The aimed alkaline peeling liquid is obtained by ordinarily adding several percentage of an oxidizing agent in case of mixing alkali liquid in a proportion of one part for one part of solder plating liquid. As the above- mentioned oxidizing agent, ClO2, halide such as chlorate and iodate, aromatic nitro compd. such as nitrobenzoic acid and nitrophenol, permanganate and bichromate, etc., are used. Further photosensitive resin unnecessitated after solder plating can be efficiently removed by this alkaline peeling liquid.