ABSTRACTIn this report, the newly developed three-dimensional magneto-optical (MO) recording scheme and the experimental results are reported. A part of this work has been done as the national project of 3D-MO (3-dimensional MO) project. It started at September 1998 and ended March 2002 as a part of the national project “Nanometer-Scale Optical High Density Disk Storage System” and aimed at achieving 100 Gb/in2 in storage density. Three-dimensional MO recording is one of the prosperous candidates of next generation ultra high density recording. Magnetic amplifying MO system (MAMMOS) is employed for achieving the novel three-dimensional MO recording. Double-MAMMOS scheme consists of 2-recording layers of differing compensation temperature (Tcomp ) and one readout layer was proposed and discussed.With write/read test it is succeeded to show the results corresponding to a 100 Gb/in2 (50 Gb/in2 × 2) recording density. We also proposed and showed results of simulations of a new type of Double-MAMMOS in which the recording layers can hold quadri-valued information by single writing process.