Paraphrasing is an important skill in academic writing -it is a cognitive skill that requires higher order thinking and high proficiency inss both reading and writing. This research explored the paraphrasing ability of EFL learners at a tertiary institution in Vietnam and examined the challenges they face when paraphrasing. Data were collected from ten second-year English major students through (i) paraphrasing a given text and (ii) individual interviews. The findings revealed that participants frequently paraphrased using synonyms, but rarely changed syntactic structures. The interviews showed that the learners encountered several language-related difficulties when attempting to paraphrase, such as inadequate understanding of the source text and the lack of vocabulary to use when paraphrasing. This paper provides insights into EFL learners' paraphrasing abilities and suggests some implications as to what EFL teachers should focus on to help less experienced student writers improve their paraphrasing skills.