Objective To explore the correlation between expression of mitogen-activated protein kinase kinase 4 （MKK4） and metastasis of oral squamous cell carcinoma（OSCC）. Methods Expression levels of MKK4 mRNA and protein were examined in surgically resected oral squamous cell carcinoma specimens and corresponding lymph nodes by semi-quantitative reverse Transcription-polymerase chain reaction（RT-PCR） and immunohistochemistry. Results The expression of MKK4 in 48 cases of metastasis of lymph node group was significantly higher than 27 cases of without metastasis of lymph node group in 75 cases of paraffin-embedded OSCC samples（P0.05）. The expression of MKK4 mRNA in 16 cases of metastasis of lymph node group was significantly higher than 22 cases of without metastasis of lymph node group in 38 cases of fresh OSCC samples（P
