In a method of measuring group delay (Tgd) of a device under test, an analog input signal having a predetermined period (T) is provided to the device under test so as to obtain a delayed output signal from the device under test. A phase difference is detected between first and second digital signals converted from the analog input signal and the delayed output signal, respectively. A current (I) corresponding to the phase difference flows through a circuit having a predetermined resistance (R) so as to result in a potential difference (ΔV). As such, the group delay (Tgd) of the device under test is determined as a function of the predetermined period (T), the current (I), the predetermined resistance (R), and the potential difference (ΔV). An apparatus for measuring the group delay (Tgd) of the device under test is also disclosed.