Red ginseng marc (RGM), a byproduct obtained during manufacturing various ginseng products, which is typically discarded as waste, contains numerous residual bioactive compounds. However, the recovery of bioactive compounds, including transformed ginsenosides, from RGM using conventional extraction techniques is difficult. In this study, subcritical water was used for a quick and high-yield extraction of the bioactive compounds in RGM. Furthermore, the chemical species and antioxidant activities of the extracts were analyzed. Extraction was performed in the temperature range and duration of 140– 200 ℃ and 15–90 min, respectively, to determine the optimal conditions for achieving the highest extraction yield and bioactivity. Under the optimized conditions (200 ℃ and 15 min), an extraction yield of 48 wt% was achieved, which was 1.8 and 4.1 times higher than those achieved via Soxhlet extraction with water and 80% ethanol, respectively (8 h). In addition, the antioxidant activity of the subcritical water extract was 2.7–78.7 times and 2.8–9.8 times higher than those of the extracts obtained using the Soxhlet method with water and 80% ethanol, respectively. The total ginsenoside content of the extract was 30 mg/g, and G-Rf, a transformed ginsenoside, was the primary component of the extract.