The voltage response of ZnO varistors to 8/20 µs surge current was investigated. The observed frontal spikes on the residual voltage waveforms are caused by the ignition gap, and no frontal spike was observed when a thyristor was used as the discharge trigger. The rear part of the waveform is determined by the damping coefficient of the RLC-circuit. Near the critical point, the residual voltage waveform changes from non-oscillating attenuation modes to distinct across zero oscillating modes along with the increase of the peak current, but there will be no oscillation happen when a thyristor is used as the discharge trigger. The residual voltage peak is not synchronized with the current peak, and the voltage peak is leading, implying that the ZnO varistor appears to be inductive. According to the experiment results, it can be reasonably explained that the voltage peak leading phenomenon is attributed to the transient skin effect of the varistor materials.