To evaluate the association between serum concentration of heavy metals and number of spontaneous abortions in Korean women in the reproductive age. Retrospective cohort study. We analyzed data of women aged 20-49 years and recruited during the sixth Korean National Health and Nutrition Examination Survey 2010-2012 (KNHANES VI). The study population was divided into four groups based on the number of spontaneous abortion (SA) experiences (SA=0, 1, 2, and ≥3). The relationships between serum concentration of each pair of three heavy metals (lead, mercury, and cadmium) and number of spontaneous abortion experiences were calculated using univariable and multivariable models. Covariates included women’s age at the time of survey, body mass index, status of alcohol consumption, status of smoking, level of education, and coexistence of chronic diseases. Among a total of 8812 women participants, 6535 were married and with a history of at least one pregnancy. The mean serum lead level was increased with higher number of SA experiences. Increase of serum lead level by one unit increased the risk for SA≥3 (adjusted OR=1.62, 95% CI: 1.06, 2.48) in the multivariable model. In contrast, an inverse relationship was found between cadmium concentration and SA=2 and SA≥3 (OR=0.57 and 0.52, respectively). This relationship was not observed for mercury. The serum lead level is associated with a history of higher number of SAs in women within normal reference. A paradoxical effect of cadmium in early pregnancy was observed. Further studies would be needed to identify potential embryo-toxic effect of lead exposure, which has been presumed to be safe.