Plagiarism, one aspect of academic dishonesty,is a serious problem and becoming morecommon in higher education. This study examinedundergraduate students at the faculty ofeconomics, Shiga University, on their knowledgeofplagiarism. Atotalof 106undergraduate students were presented with anoriginal paragraph and three rewritten versionsof the original paragraph, one of which wasconsidered plagiarized according to publishedguidelines because it included strings of wordscopied directly from the original text withproper citation but without quotation marks;another of which was considered acceptablebecause quotation marks were placed aroundthe words copied from the original text withproper citation; and the third was also consideredacceptable because the original text wasproperly paraphrased without copying exactwords or structure accompanied by proper attribution.The students were asked to compareeach rewritten version of the paragraph to theoriginal text and identify whether each versionwas acceptable (not plagiarized), indeterminable,or inappropriate (plagiarized). The resultssuggested that the students’ knowledge ofproper ways of citing and paraphrasing theoriginal text was insufficient and that their criteriafor distinguishing plagiarism andappropriate citations were ambiguous. Thesefindings suggest that some students wouldcommit plagiarism unintentionally becausethey do not understand what plagiarism is. Instructionon quotation and paraphrasing seemsto reduce the incidence of students’ plagiarismresulting from their ignorance.