Abstract: This paper introduces two independent experiments in which perceptual prominent degree (in Exp. 1) and stress type (in Exp. 2) of syllables were labeled, respectively, in a speech corpus containing 300 utterances. In Exp. 1, 60 subjects, who had no linguistic background, were divided into three groups to label the stressed prosodic units they heard, i.e. compound prosodic words in sentences, prosodic words in compound words and syllables in prosodic words,. Perceptual prominent degrees of syllables were then calculated from the results. The three authors of this paper, who are phoneticians, participated in Exp. 2, in which sentence stresses were classified into semantic stress and rhythmic stress. The perceptual prominent degree obtained in Exp. 1 provides convincing evidence for the classification of sentence stress in Exp. 2. That is to say the difference between the two stress types is perceptible by Mandarin native speakers. The final results show that (1) all stressed syllables are much more prominent than unstressed ones; (2) semantic stress is more prominent than rhythmic stress; (3) when a syllable obtained a sentence stress, it has the tendency to enhance the prominent degree of the unstressed syllable followed it, however, the difference between the prominent degree of the stressed syllable and the unstressed syllable is enlarged; (4) rhythmic stress tends to be allocated to the last syllable of the last prosodic word (or foot) in a semantic unit, while the location of semantic stress cannot be predicted from the prosodic structure of a sentence

Key words: sentence stress, rhythmic stress, semantic stress, stress prominence, stress type