Thermal stability of carbides in a new corrosion-resistant Ni-Cr-Mo alloy with high strength was studied by means of OM, SEM, TEM and chemical phase analysis. Results show that the microstructure of the alloy on standard heat treatment condition consists of equiaxed grains of f.c.c γ with an average size of 50 μm. Second phase particles of various sizes ranging from 100 nm to 2 μm are not only presented at grain boundaries, but also randomly distributed in grain interiors and were identified as the Mo6C and μ phases, respectively. After exposure for 10~1000 h at 600 °C, almost no change in their morphologies, phase particle sizes and distribution can be seen, which implies that the Mo6C and μ phases are stable during aging at 600 °C. However, their morphologies change gradually from granular to plate-like during exposure of up to 500 h at 650 °C. Beyond 500 h the Mo6C and μ phases will dissolve gradually and meanwhile, the continuous precipitates Cr23C6 are formed at the grain boundaries, which indicates that the Mo6C and μ phases are not stable during aging at 650 °C and the service temperature of the new alloy should be lower than 650 °C