Non-destructive X-ray microtomography at a third generation synchrotron facility was applied to analyze the cell morphology of microcellular polystyrene (PS)/polyethylene (PE) alloy foams. This method, differing from the observation of cross section of cell by SEM, enables one to observe a complete cell structure in the polymer foam. PS/PE foams were prepared using a supercritical CO2 foaming process. A styrene-ethylene-butylene-styrene (SEBS) copolymer was used as the compatibilizer of PS and PE to improve the cell morphology. The effects of PS/PE composition and foaming conditions (temperature and pressure) on the cell structure of foams were investigated in detail. The optimal SEBS content for the foaming of PS/PE (70:30) alloys was found to be 5 wt%. The cell size and cell density were also dependent on the foaming temperature and the saturation pressure. (C) 2013 Elsevier B.V. All rights reserved.