Objectives To reduce the incidence of mother-to-child transmission (MTCT) of HIV in Malawi, interventions have been created for women to be informed about the MTCT of HIV and for women living with HIV to be entered into the HIV care cascade to ensure safer deliveries. Our study aimed to examine the effectiveness of these strategies by exploring the determinants of adequate knowledge of MTCT of HIV among women living with HIV in Malawi. Methods We used the 2015-16 Malawi Demographic and Health Survey data and applied logistics regression analysis to explore the determinants of adequate knowledge of MTCT of HIV among women living with HIV. Results Our findings estimated that 75% of women living with HIV possessed adequate knowledge of MTCT of HIV. We also found that compared to those with no formal education, women with primary education (OR = 1.88, 95% CI = 1.04, 3.41) and secondary education or higher (OR = 2.61, 95% CI = 1.21, 5.62) were more likely to have adequate knowledge of MTCT of HIV. Furthermore, women who were resident in rural areas (OR = 2.97, 95% CI = 1.58, 5.57), were more likely to have adequate knowledge of MTCT of HIV relative to those in urban areas. Finally, women who had adequate HIV knowledge (OR = 1.85, 95% CI = 1.19, 2.89) and those who rejected the endorsement of HIV stigma and discrimination (OR = 2.30, 95% CI = 1.39, 3.81) were more likely to have adequate knowledge about the MTCT of HIV. Conclusion Based on our findings, there is an urgent need to offer women living with HIV in Malawi the opportunity to increase their knowledge of MTCT of HIV if the country is to make progress towards the elimination of MTCT of HIV as part of the overall strategy to contain new HIV infections in the country.