Abstract: Hydroxypatite is a kind of ideal orthopedic material of bone and teeth, but its low strength and brittleness need to improve. It is discovered that pure hydroxyapatite fractures in intergranular facture mode and zirconia’s toughening hydroxyapatite does in transgranular fracture mode by scanning electron microscopy observation of crack propagation and fracture surface of both materials. The mechanisms of different fracture mode are analyzed, and the toughening principle of hydroxyapatite by zirconia particles is discussed.