Plagiarism has been a growing concern among institutions and academics in recent years. To address the problem, and to alleviate the growing trend of this academic misconduct, students' perceptions of plagiarism should be considered. This study explores students' self-perception and actual understanding of plagiarism, and the relations between them. Survey responses were collected from 433 students in a Hong Kong junior secondary school. Results reveal that students show different understanding towards 'obvious' and 'obscure' plagiarism, with misunderstanding or misconception more likely arising over obscure plagiarism. This study also reports that students' self-perception on their understanding of plagiarism differed across grade levels, and their academic performance of inquiry-based learning has a relation to their self-perceived and actual understanding of plagiarism. Implications for improving the teaching and learning of plagiarism are discussed. [Copyright of Journal of Librarianship and Information Science is the property of SAGE Publications.]