The effects of magnetic properties and thickness of single-layer Co-Cr film media on perpendicular recording with a ring head are investigated. The effects of the reproducing head gap length and the reproducing head-to-medium spacing on reproduction are also discussed. Experiments are performed using ring heads for recording and reproducing and using single layer Co-Cr film media whose effective perpendicular anisotropy field Hk,eff from the in-plane hysteresis curve is greater than 5 kOe. The following results are obtained: (I) The reproduced voltage Ep at long wavelength is nearly proportional to the thickness δ of the medium and to the coercive force H_{c}(\perp) in the normal direction of the film. (2) E p is independent of the saturation magnetization M s . (3) The -6dB wavelength λ 50 is independent of δ. (4) λ 50 gradually increases as H_{c}(\perp) or M s increases. These results are well explained by a model of perpendicularly-recorded magnetization which assumes zero transition width and self-demagnetization in the medium. Calculations based on our model predict that the wavelength response of the reproduced voltage strongly depends on the reproducing head gap length and the reproducing head-to-medium spacing rather than on H_{c}(\perp) , M s and δ. An excellent high recording density (λ 50 of 0.45 μm or 113 kBPI) can be obtained by a medium and a head-to-medium interface suitable for high-density recording.