The phonation variation in Shanghainese is influenced by both phonemic phonation contrast and global prosodic context. This study investigated the phonetic realization of checked and unchecked syllables at four different prosodic positions (sandhi-medial, sandhi-final, phrase-final, and IP-final). By analyzing both acoustic and articulatory voice measures, we achieved a better understanding of the nature of checkedness contrast and prosodic boundaries: (1) Different phonetic correlates are associated with the two laryngeal functions: The checkedness contrast is mostly distinguished by the relative degree of glottal constriction, but the prosodic boundaries are mostly associated with periodicity and noise measures. (2) The checkedness contrast is well maintained in all prosodic contexts, suggesting that the controls for the local checkedness contrast are rather independent of global prosody.