Background and Objectives : Distinguishing benign from malignant lesion in thyroid noddex is important but clinically difficult. FNAB is the first investigation of choice. However, cytologic results are often indeterminable. In those cases, additional molecular biologic tests are helpful. If serologic tests are available to predict malignancy, it can be useful to fortify accurate diagnosis. We analyzed whether TSH or FreeT4 level could be used as a predictor of malignancy. Materials and Methods : From January 2008 to March 2009, 540 patients received one of thyroidectomy in a single center. We only included 167 patients from 18 to 65 years old without cardiopulmonary or renal disorders. All the patients were in euthyroid state and took no medications, which affect the thyroid function. We reviewed charts retrospectively to find out differences in TSH level and FreeT4 level between the benign and malignant groups. Results : In this study, all the patients with malignancy had the papillary cancer. In benign group, average TSH level came out to be 1.48mU/L, whereas the average TSH level of malignant group was 1.98 mU/L. Moreover, the higher the cancer stage was, the higher the TSH level was. Although we have adjusted factors that can affect TSH level(age, sex, race, goiter type), we still received the same result. The risk of malignant cancer increased in proportion with TSH level within the normal range. In free T4 level, there was no difference between benign and malignant group. Conclusion : We propose that TSH level can play a role as one of the predictors for thyroid cancer. However, there is limitation because all the patients with malignancy in this study have papillary cancer. Thus, we can apply this result only in papillary cancer, and we need more study for other types of thyroid cancer.