Khmer medicinal plants have been employed to treat human diseases for nearly a thousand years.Several studies have shown that the principal phytochem. constituents of such medicinal plants are phenolic acids, flavonoids, tannins, and alkaloids, which possess diverse bioactivities such as antioxidant, anti-inflammatory, anticancer, antidiabetic, antiallergic, and antimicrobial.In the present study, the extraction of the phytochem. constituents of Khmer medicinal plants (Dialium cochinchinense Pierre, Cinnamomum cambodianum Lecomte, Gardenia angkorensis Pitard, Cananga latifolia (Hook.f. & Thomson) Finet & Gagnep, and Oroxylum indicum (L.) Kurz bark) is performed using a supercritical carbon dioxide integrated hydrothermal process (SC-CO2-H) at a temperature of 150°C, pressure of 10MPa, water flow rate of 2mL/min, CO2 flow rate of 0.15mL/min, and extraction time of 4h.The total phenolic compounds content and antioxidant activity of the Khmer medicinal plants were determined by using the Folin-Ciocalteu and DPPH scavenging activity methods, resp.The phytochem. constituents of such plants were identified using GC-MS anal.The results showed that the extracts obtained by SC-CO2-H contained a high amount of total phenolic compounds with potential antioxidant activity.The GC-MS results also suggested that the Khmer medicinal plants contained many bioactive compounds with a broad range of biol. activities, which could be employed in the food, pharmaceutical, and cosmetic industries.