Microstructure and mechanical properties in a cast product depends on the size of the mold cast product. In this study, using three kinds of metal mold size is L-bow 1 "(Als1), L-bow 1 ½" (Als2), and L-bow 2 "(Als3). Casted metal is scrap aluminum casting furnace while the furnace crucible used is by using coal fuel. Tests were conducted with hardness test, test microstructure and chemical composition test. Results of hardness testing has been done showed that the cast product with the smallest size that is Als1 has the highest hardness value is an average of 76.82 kgf / mm ², while Als2 has an average hardness value of 73.38 kgf / mm ², and has Als3 hardness value of the average 72.57 kgf / mm ².If viewed from the testing process, showed that the smaller the size of the mold cast product, the hardness value will be higher. Similarly, the grain growth is formed, the smaller the size of a cast product, the grain growth that occurs would be even smaller.