This study investigated the perception of Mandarin tonal alternations in disyllabic words. In Mandarin, a low-dipping Tone3 is converted to a high-rising Tone2 when followed by another Tone3, known as third tone sandhi. Although previous studies showed statistically differences in F0 between a high-rising Sandhi-Tone3 (T3) and a Tone2, native Mandarin listeners failed to correctly categorize these two tones in perception tasks (Peng, 2000). The current study utilized the visual-world paradigm in eye-tracking to further examine whether acoustic details in lexical tone aid lexical access in Mandarin. Results showed that Mandarin listeners tend to first process Sandhi-T3 as Sandhi-T3 and Tone2 as both tones, then later detect the acoustic differences between the two tones revealed by the sandhi context, and finally activate the target word during lexical access. The eyetracking results suggest that subtle acoustic details of F0 may facilitate lexical access in automatic fashion in a tone language.