This paper proposes a new impulse response reduction method using harmonically varying damping considering a single-degree-of-freedom isolation system. In general, a low damping system is better than a high damping system with respect to steady-state isolation performance at high frequencies. On the other hand, as the mass of the low damping system is subjected to an impulse input, attenuation of the response is slow. In this study, an ideal variable damper is employed to achieve impulse response reduction. If the additional harmonic response caused by the variable damping and the base excitation are at the same frequency as the impulse response and with opposite-phase, the impulse response of the system can be reduced. An expression for the variable damping is developed and the reduction performance is confirmed by numerical simulation.