Abstract: Objective To investigate the expression and clinical significance of midkine mRNA in thyroid gland carcinoma. Methods RT-PCR and in situ hybridization techniques were employed to detect the expression of MK mRNA in 50 cases of thyroid gland carcinoma samples, 30 cases of benign tissue and 30 cases of normal tissue. Results MKmRNA was only detected in thyroid gland carcinoma but normal tissues by RT-PCR, it also showed that MK expression were completely different between cancer and benign tissues (P<0.01). In situ hybridization analysis demonstrated that tMK expression was mainly laid in the cytoplasm of cancer cells, which was significantly higher than the control groups (P<0.01). Furthermore, we have found that in thyroid gland carcinoma MK expression was coincidently increased with upgrade tumor classification and staging. Conclusion MK was highly expressed in thyroid gland carcinoma, and was positively correlated with the progression of malignancy disease. Our results showed that examination of MK could be a valuable marker for the clinical diagnostic purpose and treatment of thyroid gland carcinoma disease.