Abstract <p><b>Objective:</b> The study aims to develop a quantitative analysis method for coumarins in <i>Phlojodicarpus sibiricus</i> (Fisch.) Koso-Pol., a medicinal plant, to provide a complete profile of coumarin compounds in the plant, including khellactones, lomatin, and 6″-<i>O</i>-apiosylskimmin. <b>Methods:</b> A method for quantitative analysis was developed, involving the preliminary hydrolysis of the raw materials in aqueous potassium hydroxide to deacylate esterified khellactone and lomatin derivatives. This method does not affect glycosides of simple coumarins. The hydrolysis products (khellactones, lomatin) and 6″-<i>O</i>-apiosylskimmin were then analyzed by HPLC. The technique was validated for speed, accuracy, and validation characteristics. <b>Results and Discussion:</b> The developed method was tested on rhizomes and roots of <i>P. sibiricus</i> collected from three regions of Siberia (Zabaikalsky Krai, Republic of Buryatia, and Republic of Sakha (Yakutia)). The total content of coumarins in the plant materials ranged from 12.70 to 74.03 mg/g. The method demonstrated satisfactory performance and could be used for quality control and standardization of <i>P. sibiricus</i> rhizomes and roots. <b>Conclusions:</b> The study successfully developed a rapid and accurate method for the quantitative analysis of coumarins in <i>P. sibiricus</i>, which can be applied for the quality analysis and standardization of the plant’s rhizomes and roots.</p>