Polyamide (PA) was compounded with carbon fiber (CF) with various contents (0, 5, 15, 20 vol.-%) using an elastic extruder. The effect of both the carbon fiber contents and the compounding method on thermal behavior and characteristics of crystallization are studied using differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and polarizing optical light microscopy (POL). Thermal investigation was carried out under programmed cooling and isothermal conditions. The following results were obtained: (1) The crystallization temperature became higher with the increase of carbon fiber content, while the melting temperature and enthalpy were scarcely affected by the carbon fiber content. (2) The compounding methods affected the thermal behavior of composite systems. The samples that have been extruded twice have higher crystallization and melting temperatures as well as higher melting enthalpy. (3) Isothermal crystallization was observed using DSC. From the rate constant k and Avrami＇s index n, it was found that crystallization was accelerated by the presence of carbon fiber without changing the type of nucleation. (4) The polarizing micrographs showed that the nucleation of PA occurred on the surface or close to the CF.