Technical developments in high-pressure and high-temperature generation have been made, adopting a recently devised multi-anvil 6-6 (MA 6-6) assembly with tungsten carbide (WC) anvils. As a result, the pressure and temperature conditions available in a cubic-anvil DIA type apparatus have been extended to 20GPa and 2000K. Using this assembly operated in a deformation-DIA (D-DIA) apparatus, a deformation experiment to a strain of 15% on a mixture of wadsleyite and ringwoodite was successfully conducted at 16GPa and 1700K and at a strain rate of 6×10−5s−1, demonstrating potential of the present MA 6-6 assembly as an important tool to investigate rheological properties of high-pressure phases under the conditions of the mantle transition zone.