Abstract: Objective To investigate the expression of nuclear factor-kappa B(NF-κB)and matrixmetalloproteinase-9 (MMP-9) in medullary thyroid carcinoma tissue and evaluate their clinical implications. Methods The expression of NF-κB, MMP-9 in 33 MTC samples were detected by immunohistochemistry staining.Long term follow-up information was collected from patients and their survival time data was analyzed. Results After surgery operation the followed-up rate of 32 patients was 96.97%.The positive rates of NF-κB and MMP-9 were 87.9% in all MTC. The expression of MMP-9 is correlated with age, clinical stage and distant metastasis, whereas NF-κB is only closely related to clinical stages. Based on the univariate analysis, age, lymph node invasion, distant metastasis, tumor stage, radical resection by surgery and the expression of MMP-9 were prognostic factors. In the multivariate analysis, however, only age, radical resection and the expression of MMP-9 were found to be statistically significant factors. Conclusion Both NF-κB and MMP-9 were expressed in MTC tissues, but only the expression of MMP-9 in kytoplasm is an independent prognostic risk factor.