In order to reduce automobile operating costs and solve environmental problems, it has recently become an important issue to lightly design a vehicle weight. In this study, to improve the fuel efficiency of automobiles, research was conducted on weight reduction of parts using 6061 aluminum alloy material, a lightweight material. In order to design the knuckle lightweight, the material was changed to aluminum 6061-T6 alloy material instead of FCD600 cast iron material. In addition, the design shape has also been changed to have the same stiffness as the existing material. After this, the stress change was analyzed. Knuckle made of aluminum alloy reduces weight, but strength, vibration characteristics, and fatigue characteristics must be sufficiently considered. Therefore, the knuckle dynamic stiffness analysis according to the material change was compared and the stiffness of the knuckle designed with 6061 aluminum alloy compared to the FCD600 cast iron material was found to be about 30 % better because it was designed by changing the shape of knuckle made of 6061 alloys. In addition, it was confirmed that the durability was satisfied through the fatigue test, and through this, the guide for the lightweight design and the optimal design conditions for the vehicle knuckle will be presented.