國語二聲在文獻上多被描述為一調值35的高升調。然而近來不少學者發現台灣地區的國語二聲在閩南語/國語雙語語者族群中有變異的現象：一是323的降升調，二是接近31的低降調。文獻顯示這可能與語言背景(Lo, 2004)和地區(H. J. Hsu,2004)有關。然而對於國語單語語者的研究並不多。此外，性別、母音、聲調環境和句中位置也有可能影響聲調的變異。因此，本研究旨在調查台灣地區的聲調變異現象，藉由語音學實驗的方式，探究國語二聲的變異和語言背景（閩語/國語雙語語者或國語單語語者）的關係。並進一步探討其與社會因素：地區（北、中、南）、性別和語言學因素：母音、聲調環境和句中位置的關係。受試者以17-27歲的年輕族群為主。結果發現台灣地區的年輕人普遍以平調（中平調或低平調）(level)作為二聲變異的主要變體，另一較少數的變體則為低升調(low-rising)，低降調在本研究中並不明顯。這些二聲變體有可能是受到整體調域向下縮窄的影響。而閩語/國語雙語語者的確發出較多的聲調變異，特別是低升調，這可能是受到閩語聲調系統的影響。地區、性別，以及母音、聲調環境和句中位置都會影響二聲變異。本研究進一步證實二聲的聲調變異在台灣年輕族群中的發展，支持了台灣地區國語的調域縮窄的現況。 / Mandarin Tone 2 is canonically described as a high rising tone. However, recently, T2 in Taiwan was found to have other contour types: the dipping contour (323) and falling (31) variants (Fon, 1997; H. J. Hsu, 2004), with the former being considered as a normal rising tone, but the later totally losing the rising feature. Those were all found in Taiwanese (Tw)-Taiwan Mandarin(TM) bilinguals. The reasons causing this tonal variation is supposed to be relating to the language backgrounds and other social and linguistic factors from previous studies. However, no study has confirmed those correlated factors, especially the comparison between Tw-TM bilinguals and TM monolinguals. This study thus aims to discover what the T2 variation is and where it occurs. By sampling 24 subjects, aged 17-27, with half Tw-TM bilinguals and half TM monolinguals, we conducted three experiments to test the T2 in different contexts. Results showed that instead of the falling variant, more speakers produced a level variant and a small amount of low-rising variant. Besides, the bilinguals did produce more T2 variations than the monolinguals. The results indicated that language background does affect the T2 variation among young speakers in Taiwan. Moreover, the high percentage of the Level variant support the finding of a narrower tonal range of TM, compared to the standard Mandarin. Other factors, such as genders, regions, vowels, tonal environments and sentence positions were also found to have influence on T2 variations.