Abstract: Objective 　To study the relationship between PI and A I in thyroid neoplasms. To study diagnostic value of difference of PI and AI between benign and malignant neoplasm of thyroid. Methods 　expression of Ki67 antigen in 76 cases neoplasm of thyroid was examined by immunohistochemical method ( Envision) and TUNEL. Results 　① Among the 39 thyroid adenomas TA, and 37 thyroid carcinomas TC, The difference of PI and AI between 39 TA and 37 TC were significant respectively( P < 0. 05 or P< 0. 01) . ② The difference of PI between 15 FTA and 15 FTC was significant ( P < 0. 05) . The difference of A I between 15 FTA and 15 FTC was significant ( P < 0. 05) . ③ The difference of A I between 15 PTA and 15 PTC was significant ( P < 0. 01) . The difference of PI between 15 PTA and 15 PTC was nosignificant ( P > 0. 05) . ④ PI of 9 OCTA were 1. 69 ±1. 30, PI of 7 OCTC were 2. 21 ±2. 57. The difference of PI between 9 OCTA and 7 OCTC was nosignificant ( P > 0. 05) . A I of 9 OCTA were 0. 03 ±0. 10, AI of 7 OCTC were 0. 54 ±0. 63. The difference of A I between 9 OCTA and 7 OCTC was significant ( P< 0. 05) . ⑤Among the 37 thyroid carcinomas and the 39 thyroid adenomas, correlations were observed about A I and PI ( rs = 0. 595, P < 0. 01) . Conclusion 　Among the 37 thyroid carcinomas, correlations were observed about AI and PI. The increases of AI do not means satisfactory biologic behavior. PI and AI are assayed for helping to identify benign and malignant neoplasm of thyroid.