In Standard Chinese, a Low tone (Tone3) is often realized with a rising F0 contour before another Low tone, known as the 3rd tone Sandhi. This study investigates the acoustic characteristics of the 3rd tone Sandhi in Standard Chinese using a large telephone conversation speech corpus. Sandhi Rising was found to be different from the underlying Rising tone (Tone2) in bi-syllabic words in two measures: the magnitude of the F0 rising and the time span of the F0 rising. We also found different effects of word frequency on Sandhi Rising and the underlying Rising tones. Finally, for tri-syllabic constituents with Low tone only, constituent boundary showed interesting but puzzling effects on the 3rd tone Sandhi.