This study explored the effect of incredulity and particle on the intonation of yes/no questions in Taiwan Mandarin. Two types of questions were examined – ones with and without the question particle ma. Results showed that to convey incredulity, the overall pitch would be raised and enlarged. Moreover, questions without particles are significantly higher in pitch and larger in pitch range than questions with particles. This thus led to a conclusion that the degree of incredulity being expressed in questions with ma might not be as great as that in questions without ma.