Online learning has become essential in education as the spread of coronavirus 19 (COVID-19) pandemic has brought significant changes to the field. However, education should remain welcoming and supportive to all the learners as it is important to keep the students’ behavioural intention in any form of learning environment. Thus, this study is significant as online learning is leading the trend of education now. Past studies revealed that the factors of performance expectancy, effort expectancy, social influence, and facilitating conditions under the unified theory of acceptance and use of technology (UTAUT) model affect learners’ behavioural intention to use online learning. This study intended to identify the most significant factors that influence TESL postgraduate students’ behavioural intention towards the use of online learning during the COVID-19 pandemic. It also examined the relationship amongst the four factors and postgraduate students’ behavioural intention to use online learning. The participants consisted of 169 postgraduate students at a public university in Malaysia. To achieve the aim, the study utilized a survey design using a questionnaire. The results from regression analysis revealed that all of the factors have positive effects on postgraduate students’ behavioural intention to use online learning. Meanwhile, performance expectancy has the greatest influence on postgraduate students’ behavioural intention. Hence, this study concludes that the practicality and the usefulness of online learning should be highlighted by the authorities.