The HfCo7 nanoparticles were synthesized by inert gas condensation, and the particle size was controlled by the condensation pressure. The particle morphology, size and size distribution were investigated by TEM. The crystal structure and surface chemical states of the as-synthesized nanoparticles were investigated by XRD and XPS. The magnetic properties were studied by VSM. The results showed that a higher pressure during the condensation resulted in a larger size and size distribution. Moreover, a larger size also resulted in better crystallization, higher magnetization, and increased air stability, which could be attributed to their lower specific surface area.