The precipitation behavior of the secondary M23C6 carbide in Ni-Cr-W based superalloy was studied by DSC, SEM and TEM systematically. The results show that secondary M23C6 carbide precipitates from 648 to 1147 °C and it dissolves into the matrix when the temperature is above 1160 °C. The primary M6C carbide decomposes at 1349 °C and the alloy melts completely at 1400 °C. There are two morphologies of M23C6 precipitate at the grain boundaries. Coarse lamella M23C6 precipitates from 655 to 900 °C and it changes to discrete particles above 900 °C. The cooling rate has an important effect on M23C6 precipitation behavior. In addition, during the cooling process, the serrated grain boundaries are formed because of the discrete M23C6 carbide particles which precipitate at grain boundaries.