SmCo5 magnetic nanoparticles were preparaed through a simultaneous reduction of Sm(acac)(3)center dot xH(2)O and Co(acac)(3) by assistance of Cu(acac)(2) and NaBH4 in the presence of oleic acid and oleylamine as a protectant. Supplementation of Cu activated the formation of SmCo5 nanoparticles having a CaCu5 Structure, and use of NaBH4 as a reducing agent played an important role to prevent samarium and cobalt from oxidation during preparation. The mean particle diameter was 3.4 nm, having a well-controlled crystal morphology. The magnetic properties of the prepared nanoparticles represented sufficiently high coercivity and magnetization of 1300 Oe and 15.7 emu g(-1), respectively, at room temperature.