This research examines a group of thirty three Korean college students learning Japanese, and analyzes their competence in written summarization. This study makes evident the following three issues. First, few of the research participants were able to accurately interpret the sentence constructions of the original text and concisely recreate them in a summary composition. Second, the research participants often had difficulty selecting the appropriate “Communicative Units” (CU) relevant to the central meaning of the original text. Finally, study participants showed a marked difficulty in interpreting ironic usage in the original text. Such errors frequently gave rise to vague conclusions in participants’ summaries and caused the content of their compositions to deviate from the meaning of the original text. Since summarization skills require the student to make active use of their comprehension abilities while writing, it is regarded as an efficient method for improving both a learner’s comprehension and expressive abilities at the same time. For this reason, this method promises a great many benefits both to Japanese learners and to the field of Japanese education in general.