In this study, sponge cakes were prepared with 3, 6, 9, 12, and 15% red ginseng marc powder. The samples and a control were then compared in terms of quality characteristics, including batter viscosity and specific gravity, moisture content, water activity, volume index, weight, color, textural characteristics, and sensory qualities, in order to determine the optimal ratio of red ginseng marc powder in the formulation. The batter samples containing 0, 12, and 15% red ginseng marc powder had significantly higher viscosity than the other samples. Specific gravity of batter was not significantly different among the batter samples. The control group presented significantly higher moisture content as compared to the samples containing red ginseng marc powder samples. Water activity, volume index, and weight of all samples were not significantly different among the samples. In terms of crust color, lightness, redness, and yellowness of the crust samples decreased as the level of red ginseng marc powder content increased. For the crumb color, lightness and yellowness decreased, and redness increased, with increasing red ginseng marc powder content. Hardness, cohesiveness, gumminess, and springiness were not significantly different among the samples; however, the red ginseng marc powder samples had significantly higher chewiness than the control group. In the sensory evaluation, as the content of red ginseng marc powder increased, scores for color, flavor, softness, overall acceptability, moistness, and egg-flavor decreased, while scores for red ginseng taste, bitterness, astringency, and off-flavor incresed. Overall, the 3 and 6% red ginseng marc powder samples obtained fairly good sensory scores. In conclusion, the results indicate that adding $3{sim}6%$ red ginseng marc powder to sponge cake is optimal, providing good physiological properties as well as reasonably high overall consumer acceptability.