Semiconductor SnO2 nanowire arrays were fabricated by electrochemical deposition and thermal oxidizing methods based on highly ordered nanoporous alumina membrane. Their microstructures were characterized by X-ray diffraction, transmission electron microscopy, Raman spectrum, and scanning electron microscopy. The results indicate that the SnO2 nanowire array with cassiterite polycrystalline structure is uniformly assembled into the hexagonally ordered nanochannels of anodic alumina membranes. There are three phases (Sn, SnO, and SnO2) coexisting when the as-deposited assembly system is annealed at 823 K. However, only the SnO2 cassiterite phase is detected when the assembly system is annealed at 923 K.