The effects of Mo content on the microstructural characteristics and mechanical properties of a Ni–Fe–Cr based alloy with low gamma prime (γ′) volume fraction, considered as boiler materials in 700°C advanced ultra-supercritical (A-USC) coal-fired power plants, were studied in this paper. Detailed investigations reveal that the alloys with different Mo contents have similar microstructural characteristics, except the γ–γ′ misfit after standard heat treatment. The major precipitates of the alloys are all spherical γ′, blocky MC and discrete M23C6. During long-term thermal exposure at 700–750°C, the variation of Mo content has no notable influence on primary MC degeneration, precipitation and growth of M23C6 carbide. The coarsening behavior of γ′ phase of the alloys with different Mo contents all follows Ostwald ripening kinetics. The higher Mo content can decrease γ′ coarsening rate due to the increase of the activation energy for γ′ coarsening. After standard heat treatment, the tensile properties of the alloys with different Mo contents are almost same. However, the stress rupture life increases significantly with increasing Mo content, but the ductility has no obvious change. The effects of Mo on the diffusion processes, the stacking fault energy and γ–γ′ misfit are assumed to cause the increase of the stress rupture life.