Adopting Taipei as the representative of Taiwan Mandarin, this preliminary study of Mandarin leveling in Taiwan investigated the tonal leveling of Mandarin between Mandarin-Waishengren and Holo-Benshengren in Taiwan. The results indicated that the tonal leveling of Mandarin between these two ethnic groups started as early as between the first Taiwan-born Mandarin-Waishengren generation and their Holo peers, one generation earlier than the more general patterns suggested by Trudgill (Trudgill 1986, 2004). This leveling has nearly reached its completion in the following generation, taking approximately 30 years.Four factors were proposed to interpret the rapidity of this leveling–(1) the intensiveness of Waishengren immigration to Taiwan, (2) the exclusive Mandarin-only language policy, (3) the pre-established social order and infrastructure during the Japanese colonial period, and (4) the frequent contacts between Waishengren and Benshengren.