In producing thin wall ductile iron (TWDI) cooling rate must be strictly maintaned to prevent carbide formation. There are many ways to control cooling rate and one of these is through casting design, especially gating system design. This paper discusses the possibility to produce 1 mm TWDI plate and also to note the effect of gating system design to microstructure and mechanical properties. Casting design based on gating system design are made to produce 1 mm TWDI plate. The 1 mm TWDI plates will be used for fin. There are three design and coded as T1, T2, and T3. The moulds used were made from furan sand. Beside the experiment, casting design simulation with Z-Cast was also conducted to ensure the completion of producing 1 mm TWDI plate. Simulation result showed that all designs could produce 1 mm TWDI plate. Result from experiment showed that all the designs have microstructure consisting of nodule graphite in ferrite matrix and carbide. Apart from mentioned microstructure there is also skin effect. The difference between all designs lies in carbide content and skin effect width. All the nodularity exceeded 80% and nodule count exceeded 1000 nodule/mm2. Brinell hardness number for all design exceeded minimal standard given by JIG G5502. As for UTS only T2 design can exceed the minimal standard. There is a contradictive result between experiment and simulation in cooling rate.