The typical solutions to ethics of writing’ problem are strengthening ethics of writing and tightening regulations on plagiarism. But in the middle or high school, the objective of teaching ‘ethics of writing’ is that students can write ethically. So the effective solution to the problem of ethical writing is to integrate ‘ethics of writing’ as a kind of ‘standards’ with writing process as a kind of ‘practice’. This paper aims to concretize ‘writing expository text ethically’. I analysed student’s writing process and products. And I used two plagiarism detection programs to describe the characteristics of writing process according to degree of plagiarism. As the students wrote expository text from sources, their compositions were similar in text structure, contents, and expressions. But some students tried to avoid plagiarism by using some strategies―classification, summarizing, defining, adding contents. On the basis of these analysis, I organized writing knowledge and writing strategies to help students to write expository text ethically.