The aim of this study is to compare the formant displacement in the reading rate between Korean and English vowels of Korean speakers and to delineate the Korean effects on English vowels. For Korean vowels, the change from normal-rate reading to fast-rate reading makes the overall vowel space smaller. For F2, back vowels become higher and front vowels become lower. For F1, high vowels become lower and low vowels become higher. The space size of individual vowels is more overlapped in fast-rate reading than in normal-rate reading, particularly in back vowels. For English vowels read by Korean speakers, the change of reading rate makes the F2 of a back vowel higher. However, the fast-rate reading does not make the F2 of a front vowel lower differently from that of a Korean front vowel. The F1 of a low vowel becomes higher in fast-rate reading, and it makes the space of /ɛ/ and /æ/ more overlapped. The overall space of English vowels becomes smaller in fast-rate reading than in normal-rate reading, but not so much as that of Korean vowels does. These results are different from those of Gay (1978) and Fourakis (1991). The comparison of results indicates that Korean vowels affect the formant displacement of English vowels spoken by Korean speakers.