An accurate measurement technique for the impedance and modulation frequency response of photodiodes is presented. In the measurement, the photodiode is mounted on a submount, and bond wires are used to connect the electrodes of chip. The test fixture consists of a microwave probe, a submount, and bond wires, and their scattering parameter can be attained by some accurate measurements. So the intrinsic characteristics of chips can be obtained by completely removing the effect of test fixture using microwave network theory and overcome the dependency on the electrode figures in conventional methods. Experimental results for a photodiode with coplanar electrodes demonstrate the validity of the proposed technique in the region 50 MHz～16 GHz.