Abstract: Varistors and transient voltage suppressor (TVS) diodes, as two typical surge protective devices, are often used to limit voltage in the high power microwave pulse. To investigate their nanosecond pulse response and provide a scientific basis for the selection of electromagnetic pulse interference protection devices, the experimental measurement were carried out by the way of hundreds of nanoseconds and two nanoseconds risetime pulses injecting directly. Moreover, the differences of overshoot response between the varistors and TVS diodes, under different conditions of risetime and voltage amplitudes, are developed by comparative analyses, and the physical mechanism is also expatiated. The results demonstrate that the response time of both devices depend on the risetime of the injected nanosecond pulse and it increases with the increase of pulse risetime, and TVS diode has the more faster response speed for the same risetime pulses. As the amplitude of injected pulse voltage increases, the thermal accumulation in P-N junction and the breakdown speed increases, which results in a shorter response time. Furthermore, the limited voltage amplitude of varistor is a more drastic oscillation than that of TVS diode. The voltage overshoot phenomenon, in addition, is appearing before the limited voltage stability for both surge protective devices when the fast pulses being injected. The amplitude of overshoot for two typical surge protective devices increases with the injected pulse amplitude increasing, although the limited voltage amplitude is usually determined by its own protective characteristics, the overshoot voltages for different models of one kind of device have nearly the identical amplitude under the same injected pulse. Furthermore, the overshoot voltage of varistor is usually lower than its limited voltage. For TVS diodes, however, the overshoot voltage is higher than its limited voltage and the ratio of the former to the latter increases with the decrease of the limited voltage amplitude, which means that the voltage overshoot phenomenon has a more serious impact on the performance of the low-voltage TVS diode.