Imbalanced immune responses against fetus alloantigens can lead to abnormality in pregnancy. Interleukin-10(IL-10) plays key roles in regulation of immune responses against self and foreign antigens to induce tolerance to these antigens. Therefore, alteration in expression of IL-10 during pregnancy may result in several pathologic conditions such as preterm labor. IL-10 leads to a normal pregnancy via several molecular mechanisms including development of tolerogenic dendritic cells, T regulatory lymphocytes and activation of the JAK1/STAT3 pathway in the target cells. This review has collected recent data regarding the status of IL-10 expression during term and preterm deliveries and also its molecular mechanisms that lead to a normal pregnancy.