Objective:To observe the ultrastructure feature of thyroid papillary carcinoma with neuroendocrine differentiation. Methods:The paraffin-embedded tissues were used,including 103 cases with thyroid papillary carcinoma,all of which were marked with CgA,Syn and NSE by immunohistochemistry, respectively. Those 66 cases of papillary carcinoma with positive expression of CgA,Syn,NSE were examined by electron microscope. The clinical parameters included cellular differentiation degree, nucleus feature,age,psammoma,tumor diameter,metastasis of lymph nodes,tumor capsule and surrounding-tissue invasion. STATA8.0 medical statistic software was adopted in statistical analysis. Results:18.2% cases with thyroid papillary carcinoma found neuroendocrine particles under the electron microscope. Cellular differentiation degree of papillary carcinoma and the tumor size had relevance to the neuroendocrine differentiation(P < 0.05),but the other parameters had no relevance to neuroendocrine differentiation. Conclusion:The phenomenon of neuroendocrine differentiation exists in partial cases with thyroid papillary carcinoma, and the tissues of thyroid papillary carcinoma with neuroendocrine differentiation have poor differentiation and large tumor size.