Objective　To explore anatomic features and relationships of clinoid segment of internal carotid artery (ICA), and provide anatomic basis for clinic application.　Methods　By dissecting seven adult cadaveric heads perfused with red and blue latex into arteries and veins separately under the operating microscope, anatomic details related to the clinoid segment of ICA were explored.　Results　1) The diameter of clinoid segment was about (5.11±0.81)mm; the distance between the midpoints of distal and proximal carotid dural rings was (5.46±1.90)mm. The incidence of ICA cave was about 78.6%. 2) For most specimens (78.6%), ophthalmic artery (OA) was sent out above the medial one-third of the superior surface of ICA, others (21.4%) the middle one-third (no one from the lateral one-third). 3) OA originated proximally to the distal ring in 7.1%, distally in 78.6%, or closed to the distal ring in 14.3%.　Conclusions　1) Preoperative arteriogram is indispensable for clinic treating. 2) Contralateral pterional approach is valuable to expose the origin of OA. 3) OA and other structures in optic canal should be protected during circumferential dissection of the distal ring, as well the adjacent vessels and nerves when removing the anterior clinoid process.