Abstract: A method to improve the signal-noise-ratio of the sub-harmonics generated from Ultrasound Contrast Agents (UCA) by using a sawtooth signal excitation was proposed. Based on the modified Church equation, the threshold and sound pressure dependence for the sawtooth excitation were numerically calculated, and a comparison with the case' of sine excitation was made. In the measurement, a sawtooth wave and a sine wave at fundamental frequency 2 MHz and with equal sound pressure were used to drive a kind of self-developed UCA containing microbubbles, respectively. The threshold of sub-harmonic emission and the sound pressure dependence were measured. Results demonstrated that the sawtooth wave excitation can effectively enhance the sub-harmonic emission. Compared with the sine wave excitation the amplitude of sub-harmonics was improved by 13 dB, and the threshold value was decreased. The measured results were in agreement with the theoretical predictions.