Background: Although rubella is a benign dermatose in childhood, when infection develops during pregnancy, especially during the first 12 weeks, it often causes congenital rubella syndrome (CRS) resulting in abortion and severe congenital defects. Thus, the major goal of the rubella vaccination program is the prevention of congenital rubella syndrome. This study was performed to assess the seroprevalence of rubella virus infection among pregnant women in Birjand, Iran. Methods: In this cross-sectional study, one hundred serum specimens from 100 pregnant women were randomly selected in Birjand, Iran. The specimens were tested for rubella immunoglobulin G antibodies using a commercial immunoassay. Results: A total of 94% of the pregnant women were immune to rubella. According to age group, a total of 88.2% of women in the 15 - 19-year age group, 94.7% in the 20 - 24-year age group, 93.8% in the 25 - 29-year age group, 100% of women in the 30 - 34-year age group and 100% in the 35-39-year age group were immune to rubella. There was no statistically significant difference in the rate of rubella susceptibility between the groups tested. Conclusion: Although the present study showed that the level of immunity among women in Birjand is greater than the predicated critical level, but it is recommended that all the women be checked serologically for IgG against rubella virus prior to marriage and seronegative women be vaccinated against rubella.