This paper shows the lightening approach for small vehicles by developing lower arm of the hollow extruded aluminum, which is the low cost material and has closed cross section. The manufacturing cost was reduced by developing the industrial method to form the developed lower arm of the extruded aluminum by cold press, without welding. In addition, the developed method forming of the heat-treated extruded aluminum reduces the manufacturing cost more, compared to the conventional method forming before the heat treating. The structure of the developed lower arm has the wide center part receiving the coil spring and the narrow end part connecting to the vehicle body with the bush. The center part has the same cross section as the extruded aluminum, and the end part was formed by shrinking the extruded aluminum by cold press. In addition, the original expanding clinching method was developed to joint the aluminum outer tube of the bush for the prevention action against the galvanic corrosion.As mentioned above, the lightening approach for the suspension parts of small vehicles have been achieved by developing the lower arm made of the extruded aluminum with the elemental technologies of the material, structure and joint. The developed lower arm has already been adopted for the rear suspension of our passenger car, and achieves the weight lightening of 30% and the cost reduction of 22% compared to the conventional steel lower arm. In addition, that achieves the weight lightening of 50% compared to the lower arm made of aluminum by high vacuum die-casting. Hereafter, this developed approach by the extruded aluminum will be evolved widely to the suspension parts of not only passenger car but also the other small vehicles like ATV and EV commuter.