A surface treated tin-plated steel sheet which has an alloy layer formed on the surface of a steel sheet, a tin plating layer being formed on said alloy layer with a remaining exposed portion of the alloy layer having an area of 30% or more of that of the alloy layer and, formed on said tin plating layer and said exposed portion of the alloy layer, a coating film containing P and Si in an amount of 0.5 to 100 mg/m2 and 0.1 to 250 mg/m2, respectively; and a chemical treatment solution for use in preparing the steel sheet which comprises a phosphate ion, a tin ion and a silane coupling agent and has a pH of 1.5 to 5.5. The surface treated tin-plated steel sheet is free from chromium which causes problems from an environmental view point, and also is excellent in adhesion with a paint, corrosion resistance after being coated, rust resistance, and formability.