We used Optic Microscopic and Electron Microscopic to observe the formation and development of the interxylarycork in the roots of threeyearold Scutellaria baicalensis, to reveal the characteristics of interxylarycork formation and the changes of the vessels and surrounding parenchyma cells during the development of interxylarycork, in order to provide theoretical basis and experimental evidence for the formation of pithdecayed products of Radix Scutellariae.The results showed that: (1) the secondary structure of S. baicalensis root was composed of periderm, cortex and secondary vascular tissue; Interxylarycork occurred around the abnormal vessels in the xylem. First, tylosis or other substances appear in the vessels, and then some substances also appear in the parenchyma cells adjacent to these vessels. Subsequently, the normal parenchyma cells around the vessels recovered their meristematic ability and produced cork cambium, which formed interxylarycork. (2) Interxylarycork separated healthy tissues from these abnormal vessels and parenchyma cells, and the isolated tissues will gradually become dead tissues. (3) In the transection section, these small interxylarycorks can occur at different positions of xylem at the same time or successively, they gradually expand from inside to outside and connected with the surrounding interxylarycork, and finally, they formed a large interxylarycork. (4) In the longitudinal section, interxylarycorks which exist in some S. baicalensis roots within 3 cm below the root head extend downward from the head of the roots in tubular form.