Introduction: Health insurance plays a crucial role in healthcare and financial protection. Nonetheless, a considerable portion of Malaysia's low-income population lacks health insurance. This study aimed to investigate the relationship between health insurance and out-of-pocket health expenditure (OOPHE) among the low-income group (B40 households) in Malaysia. Materials and methods: The current study used data from the National Health and Morbidity Surveys (NHMS) conducted in 2015 and consisted of 18,616 B40 respondents. Ordinary least squares (OLS) regression and a two-part model were employed for data analysis purposes. The two-part model encompassed a logit regression in the first part and a generalised linear model (GLM) in the second. Results: Most B40 households are underinsured, with only 13.81% having insurance. The results also found that insured households (0.44, 95% confidence interval [CI]: 0.01%, 0.0.87%), those over 65 years old (1.00, 95% CI: 0.41%, 1.60%), utilisation of inpatient care (2.62, 95% CI: 2.24%, 2.99%), women (0.28, 95% CI: 0.20%, 0.35%), higher education (0.27, 95% CI: 0.13%, 0.42%) and retirees (1.18, 95% CI: -0.01%, 2.37%) significantly spent more on OOPHE. In comparison, private workers (-0.32, 95% CI: -0.50%, -0.14%) and self-employed individuals (-0.27, 95% CI: -0.46%, -0.08%) significantly spent less on OOPHE. Conclusion: The findings confirm that health insurance significantly increases the OOPHE among B40 households. This highlights the necessity of a national health insurance (NHI) program that is managed by the government and provides a comprehensive benefits package. NHI will achieve much better results in controlling healthcare expenditures and reducing the prevalence of catastrophic OOPHE