It is an object of the present invention to provide a cationic electrocoating method capable of producing a coating film with high filiform-rust resistance, corrosion resistance, and rust prevention and a coated article obtainable by the method. A cationic electrocoating method comprising electrocoating a surface of an aluminum substrate with a cationic electrodeposition coating composition,    wherein said aluminum substrate is subjected to a chemical conversion with a surface treating reagent not containing a heavy metal, and    wherein said cationic electrodeposition coating composition contains a sulfonium- and propargyl-containing resin composition. A cationic electrocoating method comprising electrocoating a surface of an aluminum substrate with a cationic electrodeposition coating composition,    wherein said aluminum substrate is not subjected to a chemical conversion with a surface treating reagent, and    wherein said cationic electrodeposition coating composition contains a sulfonium- and propargyl-containing resin composition. A coated article obtainable by the above cationic electrocoating method.