This study aims at identifying and classifying the most common error types in terms of linguistic classification of errors in Korean theological university and seminary students’ written work. Furthermore, this paper also tries to find some ways to prevent those errors by discussing the issue of error treatment. At this stage of this research, the pedagogical implications are directed at the level of the class. The participants in this study were a total of thirty-five university and graduate students taking TOEFL as part of their foreign language requirement. A total of 335 sentence errors were identified and analyzed based on a modified linguistic category taxonomy. In this study, the most common errors were ‘Noun Phrase’ errors, followed by ‘Verb Phrase’ errors. In other words, students made more errors on vocabulary and expression, determiners, and verbs. The findings of this study possibly suggests the existence of interlanguage and implies that the differences between mother language and target language or the absence of certain features in Korean caused difficulty in their application in English in using the correct forms. Pedagogical implications based on the findings were discussed.