Abstract: To investigate the expression and clinical significance of p14^ARF and MDM2 protein in thyroid neoplasm. Methods Immunohistochemistry (SP method) was used to detect the expression of p14^ARF and MDM2 protein in 78 cases of thyroid papillary carcinoma(PTC),34 cases of thyroid papillary microcarcinoma(PTMC) and 45 cases of thyroid adenoma. Results Significant difference of the expression of p14^ARF and MDM2 protein was observed among the three groups(P＜0.01). The positive rate of p14^ARF protein in PTC was significantly lower than that in thyroid adenoma（P＝0.002）and PTMC (P＝0.008). While the positive rate of MDM2 protein in PTC was dramaticly higher than that in thyroid adenoma（P＝0.000） and PTMC (P＝0.009). There was a significant negative correlation between the expression of p14^ARF and MDM2 in PTC and PTMC.The expression of p14^ARF was negative correlation with lymphnode metastasis in PTC. Conclusion p14^ARF and MDM2 protein probably involved in the occurrence and development of PTC and PTMC. p14^ARF may be served as adjunctive diagnosis item to determinate the biological behavior of PTC．