The purpose of this experimental study is to investigate and compare the. vowel lengths of English diphthongs and low vowels among native-English-speaking Americans with Korean college students from the Chungnam and Gyungnam provinces. Eight words and sixteen sentences were uttered five times by twenty five subjects from three groups; 1) Chungnam dialect speakers, 2) Gyungnam dialect speakers and 3) five native-English-speaking Americans. Acoustic features (duration) were measured from sound spectrograms made by the PC Quire. Results showed that the vowel lengths of English diphthongs and low vowels between native English speakers and Korean collegians of Chungnam and Gyungnam provinces were different. Comparing the average length of English diphthongs of Korean collegians with those of American natives, we can see that native English speakers tend to pronounce the English diphthongs shorter than Korean collegians do. However, native English speakers tend to pronounce the English low vowels longer than Korean collegians do. In this study we also tried to find out the differences of English diphthongs and low vowel lengths in relation to their utterance positions among American natives and Chungnam and Gyungnam dialect speakers. By the results of this experiment, we observed a lengthening effect in the three groups. However, in the pronunciation of American natives, a lengthening effect of English vowels was more clearly observed, especially in the pronunciation of English diphthongs.