In recent years, lightweight structure designs become one of the major trends in automotive industry. There are four major aspects that are considered to develop lightweight automotive structures, including using advanced materials, manufacturing methods, design optimization, and additional cost of weight saved assessment. This paper presents the development work of a lightweight subframe for a compact car using Magnesium Casting design. The subframe design needs to meet NVH, strength, and durability, corrosion, and joint strength as well. CAE tools are heavily used to generate and validate the structural performance of the design, including topology and shape optimization, static stiffness, modal, strength and durability analyses. A prototype is also built for component and field tests to validate the feasibility of this design, including component modal test, strength test, and durability test, and vehicle proving ground durability test. Furthermore, CAE vs Test correlation is also studied to validate material characterization of using magnesium alloy and CAE solid modeling scheme for all required analyses. This work concludes the feasibility of using magnesium alloy AE44 for lightweight chassis design. Finally, we were able to achieve magnesium casting subframe design 10.69 kg that meets all the structural performance with weight reduction about 32% when comparing with the current production design 15.65 kg.