We describe a simple method based on the electrospinning process to prepare heterogeneous hybrid submicronic fibers with magnetic behavior, consisting of Co nanoparticles embedded in a polyacrylonitrile (PAN) polymer. Quantity and anisotropy of magnetic nanoparticles are key parameters to improve the specific magnetic properties of fibers. We notably show that for higher Co nanoparticles concentration, their lower dispersity into the resulting fibers lead to dipolar interactions that become demagnetizing. The structural and morphological properties of Co nanodisks and of the resulting nanocomposite fibers are investigated by SEM, TEM, and EDX. The magnetic properties of the hybrid electrospun fibers have been evaluated with a SQUID magnetometer.