This paper presents an acoustic analysis of English vowel /I/. The vowel /I/ in word-final open weak syllables, so-called happy vowel, shows a tendency to undergo happy-tensing when compared to the reference vowel /I/. It is discussed whether vowel lengthening that occurs due to phonetic environments results in vowel tensing. It will be shown that happy vowel is lengthened and tensed whereas the lengthened /i/ is not more tensed. I argue that variations of happy-tensing be characterized by the different degree of vowel fronting and raising. Happy-tensing is investigated acoustically in the interview speech of six native speakers of English. Further, it is argued that the speakers of Canadian English show greater degree of happy-tensing than those of American English do. (Chungnam National University)