An adjective of Standard Chinese can expand its meaning by duplication. A duplicated adjective tends to strengthen its meaning. During the course of duplication, changes occur not only in its form but in its sound. The primary stress is given to the second syllable, which often changes to the first tone with retroflexion. A monosyllabic adjective can constitute a prosodic foot by duplication. The second syllable changes to the high level tone in order to make it more salient. The retroflexion seems to be caused by the influence from spoken Pekingese. The stress and change of tone in SC duplicated adjectives mean that SC is in the verge of changes. This study is significant because it sheds light to the in the duplicated adjectives while past studies often pay attention only to syntactic, typological, and morphological aspects of them.