An accurate RF attenuation calibration system in the frequency range of 9 kHz to 10 MHz is developed at NMIJ, to meet the demand in recent EMC regulations that require traceability of measurements to national standard. The system works based on the RF substitution technique, in which a resistive step-attenuator is used as a reference standard and a general-purpose receiver as a precision level detector. Attenuation values of the standard are determined by calibration at single frequency, i.e., 1 MHz using the NMIJ Primary Attenuation Standard system based on the voltage ratio of the IVD. The system is very simple and higher dynamic range (>100 dB) is obtained by introducing toroidal ferrite chokes in the circuit to minimize the common mode current effects.