In this paper, the vocal expressions of human emotions of anger, fear, joy and sadness are acoustically analyzed in relation to neutral speech. The features under investigation include duration, short-time amplitude, as well as pitch at both word and sentence level. The study is specially focused on word stress in Mandarin speech signals with emotion arousal. Based on the analytical results, an overall quantitative measure of the distinctive characteristics of emotional speech will be presented. Keywords: Mandarin Emotional Speech, Acoustic Analysis, Word Stress