After Mandarin education started in the 50's, Taiwan Mandarin is fixed today. Taiwan Mandarin is quite different from the Standard Mandarin that the Minister Education issued in 1932. This study investigated the 8 Taiwan Mandarin vowels from acoustic viewpoint. In addition to comparing the different vowel realizations of Taiwan Mandarin among three linguistic groups in Taiwan (Minnan, Hakka and Mandarin), the difference between Taiwan Mandarin and Peking Putonghua is also investigated. The results show that vowel realizations produced by Minnan and Hakka linguistic groups are affected by the vowel system of their mother tongue. For instance, in terms of vowel chart, vowels produced by Hakka speakers are fronter than those produced by Minnan and Mandarin speakers. The difference between Taiwan Mandarin and Peking Putonghua is that Peking Putonghua's vowel space is bigger than that of Taiwan Mandarin, and the vowels of Peking Putonghua are more distant.Generally, Chinese Empty Vowel is regarded as apical vowel. However, Tse (1990) considered it as a high, back, unrounded vowel [ui]; while Huang (1994) considered it as a central unrounded vowel [i]. Based on the Empty Vowel's X-radiography and its acoustic characteristics, the acoustic studies on Japanese [ui] and on Korean [i], we argued that the Chinese Empty Vowel is an apical vowel.