Consuming health supplements is essential to strengthen the immune systems and protect against illness, especially during health crises such as the COVID-19 pandemic. Considering the increasing number of Muslim populations worldwide and the necessity of online applications during health crises, this research aims to study the consumer's purchase intention of halal health supplement products online by examining variables influencing consumer's purchase intention. The Theory of Planned Behaviour has been applied as an underlying theory for this study, including religiosity and COVID-19 as an extension to the theory. 214 respondents participated in this study by completing the survey questionnaire via an online platform. Analysis was performed using SmartPLS4. The findings illustrate that perceived benefit is the most important indicator for Indonesian respondents, while attitude, subjective norms, and the COVID-19 pandemic are the factors that contribute to purchase intention among Malaysian respondents. The study enhances current literature, specifically in the context of halal health supplement products. Additionally, investigating the COVID-19 pandemic in the context of halal health supplements with a unique set of variables leads to a new path of study. Examining consumer behavior such as perceived benefit, attitude, subjective norms, and the COVID-19 pandemic that influence online purchase intention will provide consumer insights to marketers involved in halal health supplement products. The perspective on consumer beliefs gives directions for strategy development to businesses.