This descriptive corpus-based study aimed to investigate EFL students' use of English lexical collocations in their academic writing. The study included 120 freshmen majoring in English Studies at a state university in the southern region of Vietnam. Corpus-based tools, specifically Sketch Engine and the Corpus of Contemporary American English, were primarily employed to categorize and assess the appropriateness of collocations expressed in the students' essays. Additionally, in order to delve deeper into research-related matters, a Likert scale survey embedded with two open-ended questions was administered to the participants. The findings obtained from both quantitative and qualitative analyses of the collected data indicated that the students most frequently utilized adjective + noun collocations in their academic essays. However, the types of collocations that seemed to pose the most challenges for their usage were noun + noun, adjective + noun, and verb + adverb collocations. This was largely attributed to their limited vocabulary size, lack of collocational knowledge and learning strategies, and L1 negative transfer, which resulted in their misuse and incorrect selection of English collocations. Based on the research outcomes, important pedagogical implications have been further discussed for effective teaching and learning of English collocations to benefit EFL students' academic writing.