Glycyrrhizae Radix et Rhizoma has been extensively used by human beings as a medicinal herb as well as natural sweetener. In this study, we performed quantification analysis of three major constituents including liquiritin, glycyrrhizin, and glycyrrhetinic acid in the 70% ethanol extracts of non-processed Glycyrrhizae Radix et Rhizoma and processed Glycyrrhizae Radix et Rhizoma using a high-performance liquid chromatography coupled with photodiode array detector. The analytical column for separation of the 3 constituents used a Gemini C18 column kept at $40^{circ}C$ by the gradient elution of two mobile phase. The amounts of liquiritin, glycyrrhizin, and glycyrrhetinic acid in non-processed Glycyrrhizae Radix et Rhizoma were 2.57%, 3.52%, and not detected. After processing by roasting, the best roasting temperature and time of iquiritin, glycyrrhizin, and glycyrrhetinic acid were $160^{circ}C$-15 min (2.46%), $160^{circ}C$-15 min (3.67%), and $240^{circ}C$-15 min (0.76%), respectively.