In order to assess the number and function of macrophages in the placenta of pregnancy complicated with gestational diabetes mellitus (GDM) as well as those of normal pregnancies, placenta samples were collected from 15 GDM patients (GDM group) and 10 normal pregnant women (control group). The expression levels of macrophage markers (CD68/CD14) and inflammatory cytokines (IL-6/TNF-α) in placenta were detected using immunohistochemistry and PCR. The results showed that the number of CD68+ or CD14+ cells in the GMD group was remarkably higher than that in the control group (P<0.05), indicating that the number of macrophages in the GDM group was significantly greater than that in the control group. The mRNA expression levels of CD68+, IL-6 and TNF-α were higher in the GMD group than in the control group. In conclusion, more macrophages accumulate in placenta of pregnancy complicated with GDM, and the expression levels of pro-inflammation factors are also increased in GDM pregnancies, suggesting that macrophages and inflammatory mediators (IL-6 and TNF-α) may play an important role in GDM.