In order to prepare Ammonium Perchlorate (AP) composite propellant with a high burning rate, fine AP, of which mean diameter is less than 10 x 10(-6) m, is required. In this study, an attempt was made to prepare fine spherical AP with safety through a freeze-drying method. O/W emulsion was prepared by emulsifying with organic solvent as dispersed phase and AP solution as dispersion medium. Organic solvents used in this study barely dissolve AP and water. The emulsion was frozen with liquid nitrogen and the frozen emulsion was freeze-dried. The mean diameter (D-av[m]) of AP prepared depends on the interfacial tension (sigma[N.m(-1)]) between organic solvent and AP solution. In the case of 0.5 x 10(-2) N.m(-1) less than or equal to sigma less than or equal to 4.9 x 10(-2) N.m(-1), the relationship between D-av and sigma is expressed by the following equation. D-av = 0.18 sigma x 10(-3) The addition of surface active agents is effective for a decrease in sigma. However, foam formed on the emulsion during the preparation for all of the organic solvents used in this study except toluene. Consequently D-av deviated from the above equation and there was little spherical AP present. It was proved that the freeze-drying method is applicable as a safe preparation method for fine spherical AP.