Studies on phraseological competence have attracted researchers from different fields, particularly TESOL. However, rarely have scholars in the field studied IELTS candidates. This study intended to explore the different types of phraseological units in IELTS academic writing task 2 and probe into the IELTS candidates’ perceptions of Phraseological competence. To this end, a corpus entailing 100 essays (26,423 words) written for IELTS writing task 2 was scrutinized, through which phraseological units were extracted, and their types were identified based on Moon’s (2019) typology. In addition, semi-structured interviews were conducted with nine IELTS candidates. The results indicated that simple formulae were the most commonly used phraseological units in IELTS writing task 2. Using inductive thematic and summative content analyses, the interview data also demonstrated that IELTS candidates had varying perceptions of phraseological competence, wherein higher band score candidates appeared to have a deeper and more accurate understanding of the concept. As for the candidates’ perceived phraseological competence, they were found to under-or overestimate their own competence at using phraseology. The findings of the study can be employed in making learner dictionaries based on the phraseologies used in IELTS.