Abstract: It is an object of the present invention to provide a pretreatment method for coating the surface of metal for vehicle chassis, in which a phosphorus element is not essential, the formation of sludge is extremely small, waste water treatment is facilitated, and a chemical conversion coat having adequate adhesion and adequate corrosion resistance can be formed. A pretreatment method for coating a surface of metal for vehicle chassis comprising treating the surface of metal for vehicle chassis with a chemical conversion treating solution to form a chemical conversion coat, wherein said chemical conversion treating solution comprises zirconium in an amount of 50 to 500 ppm on the metal element equivalent basis, and at least one silane compound selected from the group consisting of ?-aminopropyltriethoxysilane, hydrolysates of ?-aminopropyltriethoxysilane, ?-aminopropyltrimethoxysilane and hydrolysates of ?-aminopropyltrimethoxysilane; and has a pH of 2 to 6.