To avoid plagiarism, students have to learn the appropriate and effective ways of source text use, such as paraphrasing, summarizing, and citation. However, few studies have investigated how learners of English as a foreign language (EFL) employ copy and paraphrase as source text use strategies in completing writing tasks involving reading material, and how characteristics of the reading material, such as genre, affect such use. This article reports an empirical study that attempted to address the issue. Eighty students from an undergraduate program of a Chinese university wrote summaries for a narrative text and an expository text. Their drafts and the source texts are compared to identify instances of retention of strings of words from sources. Analysis of the summary scripts showed that participants heavily relied on the source texts when writing summaries. The expository text elicited a larger proportion of words than the narrative text in total text borrowed, and the former also led the participants to stronger reliance on its surface structure than the latter. The less proficient group used Exact Copy more but Paraphrase less than the more proficient group. Higher level of source use -- Major Paraphrase and Maximal Paraphrase -- seems to be immune to changes in terms of genre of source text and language proficiency. Implications of these findings are discussed with reference to the teaching, learning, and assessing appropriate source text use of university level EFL learners.