This study investigates the phonetic property of Third-Tone Sandhi in Taiwan Mandarin and the effects of contextual variability. The goal of this study is to provide empirical evidence for the description of Tone 2 (T2) and Tone 3 (T3) in Taiwan Mandarin and further to account for the phonetic features of T2 and T3 in Third-Tone Sandhi Contexts. The results show that isolated T2 is different from isolated T3 in Taiwan Mandarin. Interestingly, the phonetic T2 (T2) in Sandhi Context was supported by its longer vowel duration. Third-Tone Sandhi Rule turns T3T3 into T2T3, and anticipatory dissimilation enhances the raising effect on the Sandhi.