The physical properties of the nasalized vowels have been investigated from many angles by use of the Sonagraph as the sound analyzer, associating some other measures to ascertain the effects of the characteristic features. The Principal characteristics of nasalization are found as: (1) enforcement of intensity in the region about 250c. p. s. , due to the dull resonance of the pharyngo-nasal cavity. (2) weakening of intensity at about 500c. p. s. , due to the selective attenuation caused by the resonance of the nasal cavity (antiresonance of the nasal cavity as a side channel of the vocal tract). (3) appearance of comparatively weak and diffuse components which are ascribed to the sound emitted from the nostrils. These components are interpreted as representing mostly the sound at pharynx affected by the dull and complex resonance in the nasal cavity. These three features give the perceptional impression of nasalization, and are commonly found usually in any nasalized vowel, though the relative importance of each feature depends on the vowel. If the nasal passage is closed with fingers at the nostrils when the nasalized vowels are pro nounced, the features (1) and (3) disappear, and the frequency of selective attenuation (2) is lowered. This causes an appreciable reduction of energy in the lower frequency region, resulting a distortion of the vowel color.