【Abstract】Objective To study the significance of expression of p27 in thyroid follicular tumors. Methods The tumor samples were obtained from 53 thyroid follicular tumors, and 10 normal thyroid tissues were used as a control group. p27 was detected by the immunohistochemical staining S-P method. Results The normal thyroid group had the highest expression of p27.There were significant differences in the expression of p27 between thyroid follicular adenomas (FA) and follicular carcinomas (FTC), FA had much higher expression of p27 than FTC did. There were no significant differences in the p27 staining indexes between minimally and widely invasive FTC nor between metastized and non-metastized FTC. Logistic regression showed that p27 were effective in distinguishing FA from FTC(P=0.0048). Conclusion It appears that p27 may be necessary for the malignant transformation of the thyroid follicular epithelium, which might relate to a decrease in p27. p27 detection may be helpful in distinguishing FA from FTC.