Introduction: COVID-19 lockdown has changed the eating behaviours of people, which could affect their body mass index (BMI). These changes affected meal purchasing habits of university students, depending on their household income. Thus, the current study aimed to investigate the association between eating behaviour, household income, frequency of purchasing outside meals with BMI among undergraduate students. Methods: This was a retrospective cross-sectional study conducted among 112 undergraduate students. Subjects recalled information during the first phase of COVID-19 lockdown, which was from March 2020 till July 2020. Questionnaire consisted of socio-demography, anthropometry, frequency of purchasing outside meals, and eating behaviour using the Malay version Dutch Eating Behaviour Questionnaire (DEBQ). Results: About 64.3% of subjects reported purchasing outside meals 1-2 times per week. Higher restrained eating behaviour score was correlated with purchasing outside meals about 3-4 times and >4 times a week. Normal weight students had significantly higher restrained eating behaviour score [3.0(1.1)] than those in the obese group [2.9(1.1)]. Household income had no association with frequency of purchasing outside meals. Conclusion: Eating behaviour affected BMI and the frequency of purchasing outside meals during COVID-19 lockdown. COVID-19 lockdown has resulted in tremendous changes in the eating behaviour and physical activity pattern of university students. Future studies should focus on increasing the nutrition knowledge of university students, especially on the aspect of eating out.