The present work addresses the synthesis and characterization of crystalline cobalt nanoparticles produced through a modified polyol-process conducive to the controlled formation of magnetic soft-Co structures with potential for applications in biomedicine. XRD characterization evidenced the influence of oleate and acetate species on the formation and crystal growth-inhibition of crystalline fcc-Co with controlled average crystallite sizes in the 8-10nm range. Magnetic measurements confirmed the strong influence of synthesis conditions on crystal structure and hence, on magnetic properties. As-synthesized nanoparticles exhibited coercivity values below 100 Oe and magnetization as high as 155 emu/g at room temperature. These values agreed with the soft magnetic nature of the fcc-Co phase. © 2012 American Institute of Physics.