Some Korean speakers have trouble in learning the correct pronunciation of many complex English words which have clusters in their onset and coda position. This study shows that the difficulties Korean students have acquiring English pronunciation partly come from syllable structure differences between English and Korean. We provide an analysis based on Optimality Theory (Prince and Smolensky 1993) of the syllable structure difference and suggest that Korean speakers learn the different constraint ranking between English and Korean. This will offer Korean speakers with some helpful methods which will facilitate their learning.