Acousitc rhinometry, which is based on the reflection of an acoustic signal entering the nasal cavity, is a nonivasive and objective method designed to assess the geometry of the nasal cavity and nasopharynx. For the evaluation of postural change of nasopharyngeal volume, acoustic rhinometry was performed in 27 obstructive sleep apnea(OSA) patients and 17 normal subjects at sitting and lying postures. As compared with normal subjects, OSA patients demonstrated the significant changes in volume of the nasopharynx with postural change(p<0.001). We conclude that acoustic rhinometry may be used as a helpful diagnostic method in OSA patients by comparing the postural change of nasopharyngeal volume.