This paper investigates acoustic evidence of strengthening and lengthening on domain-intial vowels in Korean, by comparing measures of F1, F2, and duration across vowels /a, e, i, o, u/ in three different prosodic domains; Intonational Phrase, Accentual Phrase, and Phonological Word. In contrary to previous findings on domain-initial vowels in the CV syllable where no prosodic strengthening effects were observed, the results of the current study confirms the presence of acoustic correlates of prosodic phrasing in the spectral and temporal dimensions of onsetless domain-initial vowels: place features are enhanced and duration is reduced in higher level domains relative to lower levels. This indicates that prosodic phrasig is manifested in vowel features as well as in those of consonants if vowels are immediately adjacent to prosodic boundaries. The findings also suggest that strengthening and lengthening are independent effects on domain-initial vowels in Korean, rejecting the undershoot hypothesis.