This study investigates the effect of the boundary on Taiwanese falling tones at domain final and domain initial positions across intonational phrase (IP), tone group (TG), word (WRD) and syllable (SYL)boundaries. The boundaries occurred at the same position within sentences produced with broad focus. The results showed that for falling tones at domain-final position, the f0 fall decreased slower before IP and TG boundaries than before WRD and SYL boundaries. In contrast, at domain initial position, the f0 fall is faster and steeper after an IP, followed by TG, SYL, and then WRD boundaries. It is proposed that f0 decreasing rate, reflecting vocal fold vibration, varies as a function of the strength of approaching and receding boundaries. At supra-segmental levels, f0 velocity decreases as the approaching boundary strengthens, whereas f0 velocity increases as the preceding boundary strengthens.