Purpose: The purpose of this study was to evaluate the prevalence of anti-thyroid peroxidase antibodies (TPO-Ab) in pregnant and childbearing-aged women in Korea. Materials and Methods: This was a retrospective study conducted in women tested for TSH and TPO-Ab at the present institution between January 2006 and January 2010. Data were collected from pregnant women and from women of childbearing age, defined as between 15 and 45 years with regular menstruation at health examination clinic. Results: A total of 349 pregnant and 358 non-pregnant women of childbearing age were enrolled. The prevalence of TPO-Ab in pregnant group was 19.7% (69 of 349), and in the non-pregnant group was 25.4% (91 of 358) (p = 0.07). TPO-Ab concentration in the pregnant group was significantly lower than that in the non-pregnancy group (p = 0.008). Among pregnant women in the first-trimester, TSH levels in TPO-Ab positive women were higher than that in TPO-Ab negative women with significance (2.59 ± 2.15 vs. 1.76 ± 1.62, p = 0.047). Conclusions: There is a higher rate of TPO-Ab positive pregnant women and women of childbearing age in Korea compared to other races.