One dimensional nanostructured magnetic materials are interesting because of their enhanced magnetic properties and potential applications such as information storage and biosensor. To prepare uniform nanostructure with controlled diameter, we have utilized porous anodic alumina template (AAT). The nanowire arrays are prepared by incorporation of monosized 10 nm magnetite nanoparticles into AAT, accompanied by thermal annealing. Transmission electron microscope and field emission scanning electron microscope showed that the nanoparticles were changed to the polycrystalline nanowire phase in AAT. The annealing procedure, which improved crystallinity of the nanoparticles and caused clustering of nanoparticles into nanowires, had a dramatic effect on their magnetic properties. For example, coercivity measured at cryogenic temperature increased from 350 to 8000 Oe after annealing. Clustering of the nanoparticles had also significant effect on the Faraday rotation spectra of the material. For example, inter-valence charge transfer transition of isolated magnetite nanoparticles vanished in wire assembles. It might be due to significant improvement of crystallinity of the wires, which might consists of enlarged Fe3O4 nanoparticles lined up in quasi-1D wires.