Blends based on the semicrystalline Poly(ether ether ketone) – PEEK and the amorphous Poly(ether imide) – PEI have been widely investigated for their outstanding mechanical, thermal and chemical-physical properties. The conformation of the PEI monomer affects the miscibility of the blends. Although the large interest in high demanding lightweight applications, foams from PEEK/PEI blend have not been considered until recently. The aim of this work was to prepare foams from PEEK/PEI miscible blends by using supercritical carbon dioxide. The role of blend composition on the density and the morphological parameters of the resulting foams was investigated. PEEK/PEI blends with different compositions were prepared. DSC and DMA analyses, performed to determine the thermal transitions and the crystallization behavior of the used, showed that blends were miscible at all composition when in the amorphous state, but they were partially miscible after an annealing process that maximized the crystalline phase in PEEK. DMA characterization was also used to define the foaming temperatures. In particular, the glass transition temperature shifting, resulting from the polymer plasticization induced by the solubilization of the physical blowing agent (CO2), was measured on all blends. Foams were prepared by means of the solid state foaming technique, which uses a fast temperature increase to induce bubbles nucleation and growth in samples previously solubilized with the blowing agent. Two sorption pressures were used to reach different CO2 uptakes. SEM analysis showed that a closed cell microcellular morphology, with average cell size between 2 and 3 μm, was obtained for all blend compositions and for the whole foaming temperature range. Higher CO2 uptake allowed a decrease of the foam density at each foaming temperature (down to 0.2 g/cm3), while a complex relationship between foaming temperature and cellular morphology (in terms of cells density and cell size) was evidenced.