Abstract: The quasi-static indentation tests of the closed-cell aluminum foam under the spherical-end cylindrical indenters were performed. The effects of indenter size, relative density and boundary condition on the indentation hardness, energy absorbing capability and energy absorbing efficiency of aluminum foam were investigated. The results show that the power function can be used to describe the indentation response curves of Al foam under the spherical-end cylindrical indenters and the index of power function linearly increases with the increasing of indenter size. Cross-sectional views of the indented specimens show that the deformation is confined to the region under the indenter with very little transverse spread, and the indentation deformation of aluminum foam is non-uniform. The indentation hardness linearly decreases with the increasing of indenter sizes, but it linearly increases with the increasing of relative density. The energy absorbing efficiency of aluminum foam is not related to the indenter size and relative density. In a certain indentation depth range, the difference between rigid foundation and simply supported conditions on the indentation response of Al foam can be ignored. Finally, the relations between the indentation hardness, energy absorption capacity, the indenter size and relative density are established by fitting the experimental data.