By supplying inorganic ferrite nanoparticles of different morphologies as nucleation sites, PANI/ferrite nanocomposites with novel coralloid structures were synthesized successfully through a simple, conventional, and inexpensive one-step in situ polymerization method without the aid of any surfactant, organic dopant, or template. As shown by XRD, FT-IR and UV-vis, there is no obvious chemical interaction between PANI and BaFe12O19 (BF) nanoparticles; that is, ferrite nanoparticles served only as the nucleation centers for the growth of PANI nanofibers, whereas the nanoparticles have an effect in reducing the diameters of the produced PANI nanofibers. PANI/BF nanocomposites are hard magnetic properties with alternative electrical conductivities and magnetic properties. The reflection loss of BF nanoparticles in 2-18 GHz was essentially enhanced upon PANI coating, and the frequency relating to maximum reflection loss shifts to a higher value with the increase in BF content because of the higher anisotropy field. With controllable electrical, magnetic, and electromagnetic properties, the prepared nanocomposites may have potential applications in chemical sensors, gas separation, catalysis, microwave absorbing, and magnetoelectric devices.