This article presents the effects of nanoclay and supercritical nitrogen on the crystallization and thermal behavior of microcellular injection-molded polyamide-6 (PA6) nanocomposites with 5 and 7.5 wt% nanoclay. Differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and polarized optical microscopy (POM) were used to characterize the thermal behavior and crystalline structure. The isothermal and nonisothermal crystallization kinetics of neat resin and its corresponding nanocomposite samples were analyzed using the Avrami and Ozawa equations, respectively. The activation energies determined using the Arrhenius equation for isothermal crystallization and the Kissinger equation for nonisothermal crystallization were comparable. The specimen thickness had a significant influence on the nonisothermal crystallization especially at high scanning rates. Nanocomposites with an optimal amount of nanoclay possessed the highest crystallization rate and a higher level of nucleation activity. The nanoclay increased the magnitude of the activation energy but decreased the overall crystallinity. The dissolved SCF did not alter the crystalline structure significantly. In contrast with conventionally injection-molded solid counterparts, microcellular neat resin parts and microcellular nanocomposite parts were found to have lower crystallinity in the core and higher crystallinity near the skin.