The melting process of NC is studied by using modulated differential scanning calorimetry (MDSC) technique, the microscope carrier method for measuring the melting point and the simultaneous device of the solid reaction cell in situ/RSFT-IR. The results show that the endothermic process in the MDSC curve is reversible. It is caused by the phase change from solid to liquid of the mixture of initial NC, decomposition partly into condensed phase products. The values of the melting point, melting enthalpy (Hm), melting entropy (Sm), the enthalpy of decomposition (Hdec) and the heat-temperature quotient (Sdec) obtained by the MDSC curve of NC at a heating rate of 10 K min–1 are 476.84 K, 205.6 J g–1, 0.4312 J g–1 K–1, –2475.0 J g–1 and –5.242 Jg–1K–1, respectively. The MDSC results of NC with different nitrogen contents show that with increasing the nitrogen content in NC, the absolute values of Hm, Sm, Hdec and Sdec increase.