Background: Out-of-pocket expenditure (OOPE) considers a barrier to access to healthcare for pregnant women. This study aimed to estimate the magnitude and associated factors of OOPE for antenatal care (ANC) in a rural Sri Lankan setting. Methods: This study was a follow-up of a large pregnancy cohort [Rajarata Pregnancy Cohort (RaPCo)] in all 22 Medical Officers of Health areas in the Anuradhapura District, Sri Lanka. A pre-tested interviewer-administered questionnaire was used to collect data on socio-demographic, economic, and the cost incurred in the first trimester, and self-administered questionnaires were used monthly to collect costs incurred in the second and third trimesters. In-depth financial information of 1,558 pregnant women was analyzed using descriptive statistics for the magnitude, non-parametric statistical methods for statistically significant difference, and the multiple linear regression model to test the associated factors. Results: The mean (SD)]age of the pregnant women was 28.3 (5.6) years. The mean (SD) monthly household income and expenditure were USD 277.29 (216.04) and USD 190.19 (103.11), respectively. The mean OOPE for per visit ANC was USD 4.18 (52.1% of per day household expenditure). The mean OOPE for total ANC was USD 57.74 (3.4% of annual household expenditure). The direct medical OOPE share (73.8%) was significantly higher than direct non-medical OOPE (26.2%) (p<0.001). Pregnant women who utilized only the government-free health services also spent 28% and 14% of OOPE on medicines and laboratory investigations. Monthly household income (p<0.001), monthly household expenditure (p<0.1), used healthcare mode (p<0.05), having maternal morbidities (p<0.05), and the number of previous pregnancies (p<0.1) were the statistically significant independent predictors of OOPE during ANC.Conclusion: Per visit OOPE for ANC is equivalent to half of the per day household expenditure. Monthly household income, expenditure, used healthcare mode, maternal morbidities, and the number of previous pregnancies are independent predictors of OOPE during ANC. Despite having freely available government health facilities, the majority tend to use private health facilities and incur higher OOPE. Government-free healthcare users also incur a direct medical OOPE for medicines and laboratory investigations.