A ceramic particle group dispersed in a solvent in a state of primary particles of single crystal, a method for production thereof and a use thereof are disclosed. In one embodiment a method is disclosed for producing a sintered particle (ceramic particle) group of hydroxyapatite (HAp), which includes a step of subjecting a system wherein calcium carbonate is present between primary particles of hydroxyapatite (HAp) to sintering and then dissolving calcium carbonate with water to remove calcium carbonate. A hydroxyapatite (HAp) sintered particle group produced by the above method is a nanometer size particle group having a particle diameter of about 70 to about 120 nm, and is a particle group having a uniform particle diameter (coefficient of variation: 12%), and further 96% of the particle group is dispersed as a single crystal particle.