FeCo nanocubes are of great interest due to their outstanding magnetic properties and larger contact area compared to the spherical particles. Herein, the FeCo nanocubes could be obtained by the reduction of metal ions by hydrazine hydrate under a concentrated basic condition. It was found that shape of the FeCo nanocubes varied from cubic with a mean edge length of 130±3 nm to polyhedron (diameter around 500–700 nm) depending on the concentration of using polymer. A lot of irregular nanoplates were also obtained when used the excessive polymer. In addition, the as-synthesized particles were air-stable which might be related to the formation of thin polymer shells on particle surfaces. The FeCo nanocubes also possessed exceptional magnetic properties at room temperature, including a very high saturation magnetization (217.14 emu/g) and low coercivity (85.95 Oe).