In producing thin wall ductile iron (TWDI) cooling rate must be strictly maintained to prevent carbide formation. There are many ways to control cooling rate BUT the most independent one is by casting design. By choosing this parameter major changes in equipment and raw material used in the foundry can be avoided. This paper discusses the effect of gating system design on microstructure and mechanical properties of 5 mm TWDI plate. A casting design based on vertical gating system is made to produce 1, 2, 3, 4, and 5 mm TWDI plates. Plate with 5 mm thickness becomes an interesting subject due to its position as the thickest and furthest from ingate in casting design with a new concept. There are three designs coded as T1, T2, and T3. These three designs were also used in making 1 and 3 mm TWDI plates of which the result has been published. The plate with 5 mm thickness will be used for automotive components. Casting design simulation for filling flow and solidification were conducted with Z-Cast. Result of flow simulation shows that the filling flow happens in two kinds. Result of solidification shows that T3 has the highest solidification rate. In the experiment, the moulds used were furan sand. Experiment result shows that all the designs have microstructure consisting of nodule graphite in ferrite matrix, no trace of carbide and skin effect are formed. Skin effect length is various for all designs. The highest nodularity is only 72% and nodule count shows only 700 nodules/mm 2. Brinell hardness number for all design is beyond standard given by JIG G5502. As for UTS and elongation none of the designs exceed the minimal standard. Experiment results confirms simulation result. Compared to the previous result nodularity and nodule count decrease and curve trends for every result are not similar.