The objective of this study is to develop the mechanical properties of AlSiCu aluminum alloy by the two-step solution heat treatment. The microstructure of gravity casting specimen represents a typical dendrite structure having a secondary dendrite arm spacing (SDAS) of 40 mm. In addition to the Al matrix, a large amount of coarsen eutectic Si phase, Al₂Cu intermetallic phase, and Fe-rich phases are generated. The eutectic Si phases are fragmented and globularized with solution heat treatment. Also, the Al₂Cu intermetallic phase is res-olutionized into the Al matrix. The 2^nd solution temperature at 525oC might be a optimum condition for enhance-ment of mechanical properties of AlSiCu aluminum alloy. (Received April 3, 2018; Revised April 9, 2018; Accepted April 13, 2018)