Objective To investigate the regulatory effect of interleukin-6 (IL-6) on the expression of indoleamine 2, 3-dioxygenase (IDO) in the early pregnant chorionic villi and decidua tissues. Methods The chorionic villi and decidua tissues of women who received induced abortion at early pregnancy were collected. The expression of IL-6 and IDO in the chorionic villi and decidua tissues was detected by Western blotting. Subsequently, 10, 50 and 100 ng/mL IL-6 was added into the chorionic villi and decidua tissues to culture for 48 hours. In addition, changes in the IDO mRNA and protein expression levels in chorionic villi and decidua tissues were detected by real-time quantitative reverse PCR (qRT-PCR) and Western blotting. Results Both IDO and IL-6 were expressed in human early pregnant chorionic villi and decidua tissues. Besides, the expression of these two proteins were positively correlated (r=0.72, 0.91). After being cultured with 10, 50 and 100 ng/mL IL-6 for 48 hours, IDO protein expression significantly increased in the cultured early pregnant chorionic villi and decidua tissues in an IL-6 concentration-dependent manner. Conclusion The expression of IL-6 and IDO proteins at the maternal-fetal interface show a positive correlation in normal physiological pregnancy, and IL-6 may up-regulate the expression of IDO.