In this report, we propose the estimation method of extreme high antenna impedance by using a RF rectifier. In the proposed method, antenna impedance can be
estimated from rectification efficiency and optimized load resistance of the bridge type rectifier connected to the measured antenna. For verification of the principle on the proposed method, the diode model with ideal switching characteristics is employed in the simulational investigations. As a result, the estimated antenna impedance of the folded dipole antenna with 1.6kohm impedance is in good agreements with 17.5 %rms error.