Abstract: This study compared the whistles recorded from captive bottlenose dolphins (Tursiops truncatus) under two different experimental conditions (swimming and training) based on the signals' frequency characteristics, and the t-test was applied for statistical analysis. The results showed that most of the signals were the sine category when the dolphins were in swimming, however, they became the upsweep category when the dolphins were received training. Furthermore, the statistical analysis indicated that the beginning frequency might not reflect the significant difference between these two experimental conditions (p=0.22), however, the ending frequency, minimum frequency, maximum frequency, frequency variation, number of turns, number of loops, number of steps, number of waves, and duration all showed the significant differences between the two experimental conditions (p＜0.05). The results may be valuable for further study on dolphin acoustics under different biological behaviors.