Introduction: The prevention of mother-to-child transmission (PMTCT) plays a major role in limiting the number of children being infected by HIV. There is dearth of studies that explored the knowledge of HIV transmission and PMTCT among women living with HIV. Methods: This was a cross-sectional, descriptive study of HIV-positive mothers receiving medical care at the adult antiretroviral therapy (ART) clinic, 68 Nigeria Army Reference Hospital Yaba. A pre-tested structured questionnaire was used to collect information from the subjects concerning their socio-demographic, knowledge of HIV transmission and mother-to-child transmission of HIV and preventive measures. SPSS v23 was used for data analysis. Results: Out of the 374 participants, 282 (75.4%) were aware that HIV can be transmitted to an unborn baby from the positive mother. Of these, 240 (85.1%) were well-informed that increase mother's viral load can increase the chances of mother-to-child transmission. 268 (95%) understood that giving of antiretroviral drugs during and after pregnancy can lower transmission risk, while 254 (90.1%) saw the use of breast milk substitutes as another prevention strategy. There was statistically significant association between the respondents' knowledge of PMTCT and their husbands'/partners' awareness of their HIV status. Conclusion: In conclusion, our study demonstrated a good knowledge of HIV transmission, MTCT and PMTCT among women who were receiving ART in our centre.