The criteria that distinguish the phonological rules from the phonetic rules based on categoricality versus gradiency have drawn considerable attention (cf. Keating, 1990; Pierrehumbert, 1990). Korean Post Obstruent Tensing (POT) rule has been claimed, based on acoustic data, to be a phonological rule and that its domain of application is an accentual phrase (AP) (e.g., Jun, 1998). This paper questions the status of POT and its domain of application based on articulatory and acoustic data. By POT, a syllable initial lenis consonant (e.g., /t/, /s/) becomes tense (e.g., /t*/, /s*/, respectively) after an obstruent coda. It is known that lenis obstruents have a longer VOT, shorter closure durations, and shorter linguopalatal contact areas than tense obstruents. To investigate if POT is really a categorical process and if its application is definable in terms of an AP, acoustic and articulatory (i.e., EPG) data of derived and underlying tense obstruents were examined in four different prosodic positions: utterance-initial, intonational phrase-initial, AP-initial, AP-medial. Sentences containing a target sequence, /VpCV/, where C=/t/, /t*/, /s/, /s*/, were produced by two Korean speakers, at normal and fast speech rates. The results will shed light on the status of POT in the grammar of Korean.