A composite coated metal sheet comprising a coated film having a low environmental impact prepared free from hexavalent chromium, and having good corrosion resistance equivalent to that provided by chromate treatment and excellent adhesiveness between the coated film and a resin layer formed on the coated film. Also, a treatment agent and a method of manufacturing the composite coated metal sheet with the treatment agent is described. The composite coated metal sheet comprises a coated film formed on a surface of a plated metal sheet or metal sheet, the coated film contains an oxide and/or a hydroxide of metal other than chromium, and an organic component comprising modified and/or unmodified functional group(s).