In this study, the impulse-voltage behavior of Ar+SF/sub 6/ binary mixtures is investigated experimentally between two parallel-plane electrodes. 1.2-/spl mu/s/50-/spl mu/s, positive-polarity, impulse voltages with different magnitudes were employed throughout the experiments. The percentage of SF/sub 6/ in Ar was varied from 10% to 90% at a total gas pressure of 50 kPa and 100 kPa. The breakdown voltage of each gas mixture was recorded at 50% breakdown probability. It is observed that the breakdown strength of Ar has increased dramatically when mixed with a small percentage of SF/sub 6/. For higher SF/sub 6/ percentages, however, the breakdown voltages did increase monotonically but not dramatically similar to the trend observed under static electric fields. Under the impulse voltages, on the other hand, the breakdown of gas mixture took place at higher voltage levels than those observed under static fields for the same conditions.