While vowel duration is known to be significantly influenced by the voicing of the following consonants, little has been found regarding environmental effects of the preceding consonants on vowel duration. This study investigates the environmental effect of both the preceding and the following consonants on vowel duration and shows that, in Korean, vowel length is affected by: (1) voicing of the following consonant and (2) phonation type (e.g., plain, aspirated, reinforced) of the preceding consonant. In the quantitative study of the durational relationship among temporal units (e.g., stop closure, VOT) and adjacent vowels, it is found that the vowel duration is correlated with the phonation type of the preceding consonant: A vowel is longer after reinforced stops, intermediate after plain stops, and shortest after aspirated stops. Unlike the anticipatory consonantal voicing effects, these progressive effects function as a cue for the three-way phonation distinction of Korean stops. The overall results indicate that to fully account for the three-way phonation distinction in Korean, it is necessary to expand the traditional approach (i.e., examining only the target consonant itself) by investigating the acoustic behavior of vocalic elements in the target's immediate environment.