Acoustic rhinometry is known to be a new method to assess the degree of nasal obstruction and the results of the nasal operation or decongestion. For evaluation of the effect of posture and decongestion on nasal patency, acoustic rhinometry was performed in 10 normal subjects before and after decongestion with postural change. In this study we used a comparative, quantitative measurement of the nasal passage geometry according to postural change after nasal decongestion by three different topical decongestants. The result shows that, each decongestant increases cross-sectional area of C-notch and nasal cavity volume and postural change may affect both of them. We conclude that acoustic rhinometry can provide a sensitive index of changes in nasal geometry.