Nasalance is used to evaluate the velopharyngeal incompetence in clinical diagnoses using a Nasometer. The aim of this study is to find the nasalance differences between Vietnamese cleft palate children and Korean cleft palate children by measuring the nasalance of five oral vowels. Three Vietnamese cleft palate children with one native speaker and ten Korean cleft palate children participated in this experimentation. The results are as follows: (1) The highest nasalance score among the Vietnamese normal vowels is the low vowel /a/; however, that of Korean normal vowels is the high vowel /i/. (2) The average nasalance score of Korean cleft palate vowels is eighteen percent higher than that of Vietnamese cleft palate vowels. There was a nasalance score of over forty-five percent among the vowels /e/, /i/ in Vietnamese cleft palate patients, and /i/, /o/, /u/ in Korean cleft palate patients. These different nasalance scores of same vowels seem cause to ethnic difference between Vietnamese cleft palate and Korean cleft palate children.