Objective To observe the expression of connexin 43(Cx43) in the placenta of patients with gestational dia-betes mellitus (GDM) and explore the role of Cx43 and Cx43-constituted gap junctional intercellular communication (GJIC) in the GDM placenta tissue. Methods The immunohistochemical method and Western blotting method were used to detect the Cx43 location and expression in the placenta tissue of GDM non-treatment group (18 cases), GDM treat-ment group(22 cases) and normal gestational group(12 cases). Results Immunohistochemical staining showed that Cx43 expressed in the cytoplasm and cell membrane of trophocytes. In the GDM non-treatment group,Cx43 positive particles mainly existed in cytoplasm and had reduced obviously. Statistical analysis showed that GDM non-treatment group had significantly lower Cx43 protein level than the other two groups (P<0.05). Conclusion Low Cx43 expression in the trophocytes of GDM non-treatment group indicates abnormal GJIC between the trophocytes, which leads to abnormal fusion and differentiation of GDM placenta trophocytes. This may be related to the adverse pregnancy of patients with GDM.