The study~1 evaluates the quantal theory by analyzing the articulatory-acoustic relations in the four Cantonese palatal vowels[i:y:i y]through investigating the sensitivity of vowel formant frequencies to variation of linguo-palatal constriction location and that of constriction size along the vocal tract length during the vowels,using KMA AG5 0 0.The articulatory-acoustic data obtained in this study show non-linear relationship between the up-down and front-back displacements in linguo-palatal constriction during the vowels and the acoustic consequences,which is similar to what the quantal theory claims.Moderate displacements in constriction location and constriction size result in large spectral changes.The level of sensitivity of formant frequencies to variation of tongue displacement is lower for the unrounded[i:i]than the rounded counterparts[y:y],suggesting the quantal nature is more apparent in[i:i]than[y:y].In general,for the Cantonese palatal vowels the levels of sensitivity of F1 to the variation of constriction location and that of constriction size are similar,whereas F2 is more sensitive to the variation of constriction size than to the variation of constriction location.The latter is similar to the articulatory-acoustic relations in the Knglish vowels reported in the previous studies. The study ~ 1 evaluates the quantal theory by analyzing the articulatory-acoustic relations in the four Cantonese palatal vowels [i: y: iy] through investigating the sensitivity of vowel formant frequencies to variation of linguo-palatal constriction location and that of constriction size along the vocal tract length during the vowels, using KMA AG 05 0 0. The articulatory-acoustic data obtained in this study show non-linear relationship between the up-down and front-back displacements in linguo-palatal constriction during the vowels and the acoustic consequences , which is similar to what the quantal theory claims. Moderate displacements in constriction location and constriction size result in large spectral changes. the level of sensitivity of formant frequencies to variation of tongue displacement is lower for the unrounded [i: i] than the rounded suggesting the quantal nature is more apparent in [i: i] than [y: y] .In general, for the Cantonese palatal vowels the levels of sensitivity o f F1 to the variation of constriction location and that of constriction size are similar, where F2 is more sensitive to the variation of constriction size than to the variation of constriction location. latter latter similar to the articulatory-acoustic relations in the Knglish vowels reported in the previous studies.