Synchrotron X-ray microtomography (SPring-8, Japan) has been used for the microstructure characterization in a closed cell Al-Zn-Mg alloy foam. Some sophisticated microstructure features, such as micropores and intermetallic particles inside the cell wall, were visualized and quantified three dimensionally(3D) by the high-resolution phase contrast imaging technique. By microtomographies tuned to energies above and below the Zn K-absorption edge, the 3D quantitation of Zn distribution was obtained using subtraction imaging technique. It has been clarified that the Zn distribution was inhomogeneous in the cell wall of the foam. And the agglomeration of Zn-bearing particles was confirmed to induce the brittle fracture of cell wall. The distributions of Ti and Ca in the foam were also visualized by subtraction method. The current tomographic techniques provide novel solutions for the 3D microstructure analysis in the highly inhomogeneous foam materials.