Tantalum oxynitride powder with a baddeleyite crystal structure was synthesized and densified by hot pressing in Ar and under high pressure using a belt-type high-pressure apparatus. The tantalum oxynitride powder could not be densified completely under hot-pressing conditions at 1400 degrees C. The use of high pressure resulted in dense materials. The samples showed a hardness of 16-17 GPa and a fracture toughness of 3-4 MPa.m(1/2). The hardness is higher compared with that of ZrO2 and HfO2 ceramics. The fracture toughness corresponds to the value of fully stabilized ZrO2 due to the absence of any transformation toughening mechanism.