The chief purpose of this article is to trace Chinese learners’ developmental steps for pronunciation with Korean single vowels in order to find out one of the interlanguage systems of L2 learners. This writer is in the process of investigating what interlanguage developmental steps their Korean pronunciation goes through from the entire steps of Chinese learners’ learning of Korean in general. This article traced Chinese learners’ developmental steps for single vowels. The subjects of the experiment in this study are total 10 persons, 5 men and 6 women. They have never stayed in Korea before, and they entered Korea in March, 2010 and started to learn Korean from the beginner’s 2nd level in the spring semester in April, 2010. Those learners’ average age is 21.6. According to the research, they did not get any more additional pronunciation education other than the hours fixed in the regular curriculum. The experiment was conducted with all three sessions with the intervals of six months. The 1st experiment was performed in June, 2010 when the learners completed the beginner’s 2nd level. And the 2nd experiment was conducted after six months from that in December, 2010 when they finished the intermediate level. And the 3rd experiment was performed in June, 2011, and this corresponds to the advanced level. Recorded material is about 8 single vowels in Korean (이/애/에/으/어/아/우/오), and before the experiment, the script was distributed to the subjects, and they were made to practice it. At the place for recording, there were only the experimenter and the subjects, and a notebook computer and a digital recorder recorded it at the same time. Each of the vowels was pronounced three times. The single vowels recorded were used to calculate the F0, F1, and F2 values by using Praat. The central part of the single vowels was set as the stable section of the formant, and the F1 and F2 values were calculated. The values gained in this way were arranged by drawing a vowel triangular diagram with the Excel program for each of the subjects. For each of the vowels, the Excel program was used to arrange the distribution chart with a graph. This was to examine the difference between Koreans’ vowel formant and Chinese’ distribution in their vowel pronunciation. According to the experiment result, Chinese learners show Korean single vowel pronunciation with the following developmental steps:First, in this experiment, they were asked to pronounce the same vowel three times. Though there was some difference among the subjects, when their three pronunciations were marked on the collection chart, they were quite spread in the 1st experiment but tended to gather in one place gradually from the 2nd to 3rd sessions. This implies that the subjects came to pronounce Korean vowels stably. Second, about the Korean vowels not existing in the Chinese phonemic system, vowels pronounced differently (distinction between ‘으’ and ‘어’, ‘애’ and ‘에’), and the vowels with different aspects from Korean’s in the collection chart regarding contrast (Chinese’ /u/ and /o/), the learners showed deviations in increasing the pronunciation accuracy. Some of the learners could not distinguish the contrast of certain pronunciations until the advanced level, which gives some implications to the establishment of teaching-learning strategies. Lastly, most of the learners could hardly distinguish ‘애’ from ‘에’. This may not be unrelated with the phenomenon that in the Korean phonemic system, the two phonemes join together. The writer conducted the single vowel research along with the diphthong and consonant research and is currently on the process of analysis on it. This kind of research should take the pursuit method on account of its characteristics, and it is needed to conduct the collection and analysis of voice data. In conclusion, this study is significant in that it traces the entire process of interlanguage development built in the process that foreign learners learn Korean to figure out the characteristics of each step and furthermore draws Korean teaching methods right for the characteristics of each step so that they can be applied in the actual spots of education.