In this study, I analyzed what rhetorical citation type students most frequently used when reinforcing logic of their opinions and arguments in research papers, and compared these rhetorical types between higher and lower Korean proficiency levels of students. These 30 student papers included the following rhetorical citation types: statistics, attribution, exemplification, statement of use, establishing connections between sources, and comparing one’s own findings or interpretations with other sources. Statistics was the most frequently used rhetorical citation type. In addition, the group with the highest level of Korean proficiency used citations about 8 to 11 times in their papers, and incorporated a variety of citation types including attribution, statistics, exemplification, and statement of use. Lower level students used significantly less citations and citation types. Therefore, it is necessary to raise awareness that “citations” is an important strategy to reinforce one's own logic, teach various types of citations as important research writing strategies, and prepare a more citation-focused academic writing curriculum.