Hole expansion process (HE) of metallic sheets is used to the manufacture of many products like parts for the household appliances, automotive, medical and electrical industries. Due to the importance of brass and aluminum in the sheet metal industry, the present work presents an experimental investigation of the formability in the HE process of 2-ply sheet (brass supported by an aluminum sheet) using a ball-shaped punch. The main objective of is to investigate the effects of the pre-hole diameter, type of support on the forming loads, occurrence of maximum load, limiting expansion ratio (LER), and fracture modes. 1 mm thick brass and 3 mm thick w Aluminum were used. Holes were drilled in the specimen center on an upright drill. Hole diameters were 3, 6, 8, 10, 12 and 14 mm respectively. Uniaxial tension, cupping tests and HE experiments were performed for brass supported either by blind or holed Aluminum sheet. Results showed that the force required to expand the hole, the position at which the maximum force was reached, fracture mode and forming limits were dependent on the pre-hole diameter and type and condition of support. It was concluded that in HE of brass specimens supported by (either a blind or holed) Aluminum sheet, the force required to expand the hole and the position at which the maximum force was reached decreased as the pre-hole diameter of the brass specimen increased. Fracture mode proved to depend on the type of support (blind or holed) and the hole diameter in both brass sheet and supporting Aluminum sheet. Forming limit curve (FLC's) could be constructed for the range of hole diameters in both brass and Aluminum sheets showing safe and unsafe regions in the HE process assuming two criteria: occurrence of failures in the brass sheet and occurrence of failures in the supporting Aluminum sheet. Such curves are of distinguished industrial importance in determining the success or failure in the HE process.