ObjectiveTo provide anatomical data for the operation of parapharyngeal space via endonasal endoscopic approach.MethodsAnatomic study was performed in 4 formalinsoaked adult cadaver heads (8 sides) by mimicking endoscopic surgery of parapharyngeal space via endonasal approach. In the study, the safety margin of the surgical field was evaluated, the important anatomic landmarks and their relationships were observed, and the relevant anatomic data were measured.ResultsThe length of pterygoid canal was 14.50±1.77 mm, and the distance between isthmus of Eustachian tube and internal carotid artery was 11.04±1.08 mm.ConclusionsThe prestyloid space can be exposed via endoscopic endonasal approach with proper protection of internal carotid artery (ICA). For the protection of ICA, it is essential to expose ICA below the imaginary line from external aperture of carotid canal to foramen lacerum.