Astragalosides are among the most predominant of the bioactive compounds in the root of Astragalus membranaceus and are differentially concentrated depending on the anatomical part of the root in question. The aim of this study was to analyse astragaloside contents in the periderm, cortex, and xylem of A. membranaceus root, and to compare the contents between peeled and unpeeled roots. Total astragalosides in the periderm were about 8-fold more concentrated than in the cortex, and 28-fold more concentrated than in the xylem. The dry weight percentages of total astragalosides in primary roots were 43.5% in the periderm, 47.2% in the cortex, and 9.30% in the xylem. Furthermore, unpeeled main (primary) roots were enriched in astragalosides by 1.46-fold compared with peeled main roots, whereas unpeeled lateral roots were enriched by 2.33-fold compared with peeled lateral roots. In conclusion, the periderm is the most astragaloside-rich part of the root of A. membranaceus. Therefore, it is necessary to preserve the periderm in order to supply astragaloside-rich roots for use as health food supplements.