The expression of Toll-like receptor 4 (TLR4) in neonatal cord blood mononuclear cells (MNCs) and serum TNF-α were investigated in order to explore the roles of TLR4 in the pathogenesis of preeclampsia. The study enrolled 27 patients suffering from preeclampsia (experimental group) and 21 normal pregnancy patients (control group). After MNCs were separated, the expression of TLR4 mRNA and protein was detected by using real-time quantitative PCR and Western blotting respectively, and the expression of TNF-α by using ELISA. The results showed the TLR4 mRNA level in cord blood MNCs (2(-ΔCT): 0.07±0.17), TLR4 protein expression level (absorbance ratio: 0.81%±0.15%) and TNF-α level (9.5±1.73 pg/mL) were all increased in experimental group as compared with control group with the differences being statistically significant (P<0.05). There was a positive correlation between the expression of TLR4 mRNA and TNF-± in both experimental group and control group (r=0.54 and 0.53, respectively, P<0.05). It was concluded that TLR4 expression in the experimental group of cord blood MNCs was increased and there was a positive correlation between the expression of TLR4 mRNA and TNF-α in both groups. TLR4-mediated release of inflammatory cytokines may be one of the important reasons leading to preeclampsia.