Background: Plants of the genus Achillea are widely used in both traditional and modern medicine and are known to be rich in biologically active secondary metabolites. Numerous phytochemical and histochemical studies have been con ducted on Achillea millefolium L.; however, Achillea asiatica Serg., which is widely distributed in Mongolia, remains comparatively underexplored. Therefore, investigating the distribution of biologically active compounds, the content of polyphenolic compounds, and the optimal extraction conditions of this species is of significant scientific and practical importance. Aim: The aim of this study was to identify biologically active compounds in Achillea asiatica Serg. using histochemical methods, to determine the content of polyphenolic compounds and optimal extraction conditions, and to evaluate the total and internal absorption coefficients of the plant raw material. Materials and Methods: The aerial parts of Achillea asiatica Serg. were collected in August 2025 from Erdene soum, Tuv province, Mongolia. Histochemical analysis was performed on transverse stem sections and flower petals using potassium dichromate, ferric chloride (III), methylene blue, Lugol’s iodine, and Dragendorff’s reagent, followed by ob servation under a light microscope. The total polyphenolic content was determined using the Folin–Ciocalteu method and expressed as gallic acid equivalents. Extraction experiments were conducted using powdered plant material sieved to par ticle sizes of 1, 2, and 3 mm and extracted with 20–80% ethanol. In addition, the total and internal absorption coefficients of the plant material were determined according to standard procedures. Results: Histochemical analysis revealed the presence of essential oils, polyphenolic compounds (tannins and flavo noids), and starch, while alkaloids were not detected. Polyphenolic compounds were observed in both stems and flow ers, with more pronounced accumulation in the vascular tissues. The highest total polyphenolic content (0.421%) was obtained from the 1 mm particle-size fraction extracted with 70–80% ethanol. Using 60% ethanol, the total absorption coefficient of the plant material was determined to be 5.74, and the internal absorption coefficient was 1.885. Conclution Achillea asiatica Serg. is rich in polyphenolic compounds, and their anatomical distribution is closely as sociated with the plant’s protective and biological functions. The use of 1 mm particle-size material and 70–80% ethanol was identified as the most suitable condition for extracting polyphenolic compounds. These findings provide a scientific basis for the standardization of Achillea asiatica Serg. as a medicinal and phytopharmaceutical raw material and support its further pharmacognostic and phytochemical investigation.