Background: Rubella is a self-limiting disease that causes congenital rubella syndrome (CRS) when rubella virus (RV) infects women in the first trimester of pregnancy. Objective: To assess a population of pregnant women attending antenatal clinics in two tertiary hospitals in southwestern Nigeria for anti-RV IgG and IgM in order to determine the proportions susceptible to the viral infection and infectious to their fetuses. Method: Ninety consenting pregnant women were consecutively recruited and aseptically bled for the study. The sera were screened with commercial ELISA kits for anti-rubella virus IgG and IgM. Due to the controls and calibrators included in the tests, the IgG test was performed on 89 sera while all 90 samples were screened for IgM. Results: Of the 89 pregnant women tested for anti-RV IgG, 86 (96.6%) were positive with protective serum concentrations of the antibody. Only six (6.7%, 95% CI: 1.5-11.8%, n = 90) women were positive for anti-RV IgM with 5 (5.6%, 95% CI: 0.8-10.3%) having both anti-RV IgG and IgM. Overall, three (3.4%) of the women were susceptible to RV infection, one (1.1%) of these in the first trimester of gestation was probably infectious. Conclusion: Majority of the pregnant women had protective levels of anti-RV IgG antibody although susceptibility to rubella as well as level of infectiousness were low. Intensification of rubella immunization of all females of child-bearing age in Osun and Oyo States is advocated.