Introduction Knowledge of HIV status in South Africa (SA) is reported to be 90% among people living with HIV. National level estimates could mask population-specific levels, which are critical to monitor program coverage and potential impact. Using data from the 2017 national antenatal sentinel survey, we assessed knowledge of HIV-positive status, initiation of antiretroviral therapy (ART), and socio-demographic characteristics associated with knowledge of HIVpositive status prior to the current pregnancy among women attending antenatal care. Methods Between 1 October and 15 November 2017, a nationally representative sample of 32,716 pregnant women were enrolled from 1,595 public health facilities selected from all districts of SA. Data on age, gravidity, knowledge of HIV-positive status and ART initiation prior to pregnancy were extracted from medical records. A blood sample was collected from each woman regardless of prior knowledge of HIV status or ART history, and tested for HIV in the laboratory. All HIV-positive pregnant women enrolled in the survey were eligible for inclusion in the analysis. Multivariable survey logistic regression was used to examine factors associated with knowledge of HIV-positive status prior to the current pregnancy. Results Of 10,065 eligible HIV-positive women, 60.8% (95% confidence interval (CI):59.9%-61.7%) knew their HIV status prior to the current pregnancy, of whom 91.1% (95% CI: 90.4%-91.7%) initiated ART prior to the current pregnancy. Knowledge of HIV-positive status was lower