Polycarbonate (PC)/multi-walled carbon nanotube (CNT) nanocomposites were prepared using a Haake internal mixer. The neat PC and nanocomposites were further soaked under supercritical CO2 (scCO(2)) atmosphere for various periods to develop microcellular foams. Morphological results confirmed the fine dispersion of CNTs in the composites, resulting in superior thermal stability (44 A degrees C increase at 5 wt% loss) and dynamic storage modulus (22 % increase at 75 A degrees C) compared with the neat PC. The composites exhibited a rheological percolation threshold at 2 wt% CNT loading. The microcellular structure of foamed samples revealed that longer soaking periods (a parts per thousand currency sign2 h) in scCO(2) resulted in larger cell sizes, and higher CNT loadings caused higher cell densities at similar soaking periods. Foaming-induced PC crystals were verified through differential scanning calorimetry and X-ray diffraction. More crystals (up to 38 %) were developed with increasing soaking time. The added CNT facilitated the crystallization of PC and obtained crystals with higher stability. The two-melting phenomenon exhibited by the foams represented the melting of the originally less-stable crystals and heating-annealed crystals. The neat PC foams or low CNT-loaded composite foams demonstrated improved thermal stability compared with their unfoamed counterparts.