Objective To investigate the role of Toll-like receptor 4 (TLR4) in lipopolysaccharide (LPS)-induced preterm delivery by analyzing the CD86 and CD69 expression in lymphocyte subgroups of mice. Methods LPS was administered intraperitoneally to establish a mouse model of preterm delivery, with or without TLR4 blockade. The incidences of preterm delivery and fetal death were calculated in each group (LPS group, TLR4 blockade group, and control group). The percentages of blood CD45+CD86+, CD3+CD69+, CD19+CD69+ and CD49b+CD69+ subsets were measured by flow cytometry. Results The incidences of preterm delivery and fetal death in LPS group were significantly higher than those in the control group (50.0% \[8/16\] vs 0\[0/16\]; 11.0%\[9/82\] vs 3.1%\[5/163\], P<0.01 or 0.05). The incidences of preterm delivery(6.3%\[1/16\]) and fetal death (3.9%\[6/154\]) in the TLR4 blockade group were significantly lower than those in the LPS group (P<0.01 or 0.05). TLR4 blockade almost completely abrogated LPS-induced increase of CD45+CD86+, CD3+CD69+ and CD49b+CD69+ cell proportions (P<0.01). Conclusion Interaction between LPS and its receptor TLR4 triggers the mobilization of CD86+ dendritic cells, which subsequently activates blood T cells and NK cells and plays an important role in preterm delivery.