The present invention relates to a chemical solution for forming a silver film on a substrate. This chemical solution has (1) an ammoniac silver nitrate solution; (2) a reducing solution containing a reducing agent and a base component; and (3) an additive containing a compound of a polyvalent metal. This additive is contained in at least one of the ammoniac silver nitrate solution and the reducing solution. The present invention further relates to a process for forming a silver film on a substrate, using the chemical solution. This process includes (a) bringing a hydrochloric acid acidified stannous chloride solution into contact with a surface of the substrate, thereby conducting a pretreatment of the surface; (b) bringing another ammoniac silver nitrate solution into contact with the surface of the substrate; and (c) bringing the ammoniac silver nitrate solution into contact with the reducing solution, on the surface of the substrate, thereby forming the silver film. It becomes possible to form a compact, uniform silver film with a high silver plating rate that allows the obtaining of high-resolution reflected images, excellent adhesion to a glass substrate, and improved corrosion resistance of the silver.