A flexible disk medium composed of Co-Ni-Mn spinel ferrite fine particles was investigated in order to confirm its high-density recording performance. This medium was prepared from particles with a mean size of 25 nm using a spin coater without burnishing. The average surface roughness and particle size of the coated disk were approximately 20 and 34 nm, respectively. The recording characteristics were measured on a spinstand tester at a rotating speed of 2940 rpm, using a floating MIG head for writing and reading. The linear recording density at 50% of maximum output was 52 kBPI, whereas that of commercial zip media (Fe-Co particles) was 67 kBPI. The overwrite performance is very important for high-density recording, and it was better than 28 dB, which was close to the results for zip media at 1 MHz. The carrier-to-noise ratio for this disk was 32.2 dB after writing a 10 MHz signal, while the signal-to-noise ratio was 20.2 dB with the band width of 50 MHz, after writing a 20 MHz signal. The resuls of experiments showed that the Co-Ni-Mn spinel ferrite disk has potential for use in high-density data storage tapes.