Closed cell metal foams have attracted a lot of attentions in recent years and have especially been used in light weight high specific strength structures. Properties of these foams depend on the characteristics of the base alloy, the relative density of the foam, the shape and size of the cells, the properties of the space holder materials and their structural defects. In this research, fabrication and characterization of syntactic closed cell Al-4.5wt%Cu alloy foam by infiltration method using ceramic hollow sphere space holder was considered. For this purpose, first the molten alloy was infiltrated in preforms made of alumina hollow spheres of different average diameters (2-5 mm) through a gas pressure infiltration method. The effects of infiltration temperature and pressure, amount of alloy, diameter of the ceramic spheres and grooving at the bottom of the ingots on the melt penetration and structural defects of the fabricated foams were investigated. Based on the results, 725 °C and 1.5 bar were selected as the suitable infiltration temperature and pressure for fabrication of closed cell foams. The selected pressure was the threshold pressure for breaking the oxide shell around the alloy ingot and overcoming the penetration resistance of the ceramic preform. The selected temperature was also the threshold temperature providing sufficient fluidity for the melt to penetrate into the ceramic preform. Lower temperatures and pressures would cause incomplete infiltration, and higher temperatures and pressures would increase the probability of formation of other structural defects and increase the energy consumption. The amount of alloy used had a significant effect on the number of filled ceramic spheres in the fully penetrated foams. It was also found that grooving of the ingots had no significant effect on the infiltration process. The highest volume percentage of the space holder obtained and, consequently, the lowest foam density achieved, were about 76% and 1.6 g/cm 3 , respectively, for ceramic spheres with an average diameter of about 4 mm (the largest ceramic spheres used). The highest compressive strength and energy absorption of about 40 MPa and 19 kJ/m 3 were obtained for the foam made with the smallest ceramic spheres (average diameter of about 2 mm) which had 63 volume percent of ceramic space holder. Hardness tests showed that presence of ceramic spheres did not have a significant effect on the hardness of the metal matrix. The hardness around the ceramic-metal interface was about 59 Vickers. Keywords : Al-Cu closed cell foam, Ceramic hollow spheres, Infiltration, Density, Mechanical Properties