The aim of present work was to find out the optimum combination of extraction process variables of hypericin from St. John’s wort, by revealing the mathematical functional relation of extraction temperature, ethanol concentration for the extraction yield, and to develop a validated HPLC method to determine hypericin in St. John’s wort extracts prepared. The HPLC separation was performed on a Luna C18 column (4.6 mm×250 mm, 5μm particle) using a mobile phase consisting of 2.5g•L-1 KH2PO4- methanol (5:95 v/v) eluted in an isocratic mode, a flow rate of 1.0 ml/min, and a detection wavelength of 588 nm. The method is validated with respect to accuracy, precision, linearity, and limits of detection and quantitation. The experiments were carried out according to a five-level, two-factor Central Composite Design (CCD) with extraction temperature and ethanol concentration as variables while extraction yield as response. The optimum process was obtained through response surface methodology (RSM) based on the mathematical model established according to the experimental data, i.e. extraction temperature: 90 °C; ethanol concentration: 77%. Under the conditions above, the mean value of observed extraction yields(n=3) was 0.6767 mg/g of St. John’s wort powder tested, with the deviation of 1.7% from the predicted value of 0.6654, which demonstrated that the mathematical model established in this study has satisfactory predictability. On the basis of result obtained, it was concluded that central composite design is a good approach to optimize the extraction of St. John’s wort.