This paper`s aim is set up a vowel system in the Anmyeon island dialect. A method of the study is to examine phonetic form of /o/,/y/, to suggest phonetic form of [oi] : [ui] and the place of articulation of [e] : [e2], [y] : [i] on the vowel system by phonetic analysis. The results of this study as follows.. (1) In the phonetic form, the `o` of phonetic form is [e] that is connect up consonants /k,n,t,t^h , t`, tf, s/. and is [oi] or [e] that is combined with a vowels. The `y` of phonetic form is [y] that is connect up consonants /k, n, t, t^h , t`, t∫, s/. and is [ui] or [i] that is combined with a vowels. (2) When `o` or /y/ is pronounced by the diphthong, `o` and `y` are sounded by each other [oi], [ui]. In the precedent studies they are described ty [oj], [uj]. But in the spectrogram analysis [o] or [u] of them are not glide, but core vowels. So, [oi], [ui] are made up two vowels in this dialect. (3) Korea alphabet -`ㅔ` and `ㅚ`- are gronounced by [e] in this dialect. So, I am carried to an experimentation in order to suggest that both of [e] have some differences of the place of articulation. As the results, both of [e] haven`t a difference. they are belong to a same category. Korea alphabet -`ㅟ`-, is pronounced by [y] or [i] in this dialect. So, I am also carried to an experimentation in order to represent that [y] and [i] have some differences of the place of articulation. As the results [v] and [i] have a difference. F1 haven`t statistically a difference, but F2 have a difference. That is to say, [y] and [i] are not belong to a same category. They are distinguished by round. respectively [y] is a round vowel, [i] isn`t a round vowel. (4) The vowel system was made up nine phonemes ; /a,a,o,u,i,ι,e,ε,y/. The [φ] may not function a phoneme in this dialect. Which belong to /e/ category. to sum up this part, the fort-round vowels are unstable in the vowel system.