Highly ordered anodic alumina oxide (AAO) membranes with a diameter of about 50 nm are prepared by two-step anodization. Cobalt nanowires were obtained by ac electro-deposition of Co2+ into the pore of AAO membranes. Vibrating sample magnetometer (VSM) results show that such a sample has highly perpendicular anisotropy properties. Here, we first use magnetic force microscopy (MFM) to obtain a fine image of magnetic domain structure in Co/AAO film successfully. MFM images show that each as-prepared nanowire in the membrane show single domain structure. The nearest neighbor bits have opposite magnetization. The magnetic moment was aligned in the same direction after the sample was magnetized under a 1 T external field. Due to its high bit density (up to 100 Gbits/in.2), such a material may be used as high-density perpendicular recording quantum magnetic disks (QMD).