Supercritical fluid extraction (SFE) with neat CO₂ was optimized for selective removal of hyperforin and adhyperforin from St. John’s wort. High extraction efficiencies were achieved when the fluid density was 0.60 g ml⁻¹ or above. The maximum extraction efficiency of hyperforin and adhyperforin could be achieved with a very mild condition such as 30 °C and 80 atm (density = 0.64 g ml⁻¹). Under these conditions, the amount of hyperforin extracted was comparable to the results of conventional solvent-based extractions (ultrasonic or boiling). The maximum quantity of hyperforin extracted from the St. John’s wort was around 12 mg/g dry plant and the reproducibility of the SFE method was comparatively good (RSD = 10%). Hyperforin and adhyperforin were isolated from the crude SFE extract (using HPLC) with purities of 98.7 and 93.3%, respectively. The identity of the isolated hyperforins was confirmed by NMR and MS methods.