Objective To study the clinical efficacy of cell block yielded by ultrasound-guided fine needle aspiration in the early diagnosis of thyroid cancer and differential diagnosis of thyroid follicular tumor.Methods Cytological smears were performed in 864 thyroid nodules by ultrasound-guided fine needle aspiration.Then the residual specimens were made as cell blocks.Diagnosis was made by observation of the organization structure of the cell block.Cell block sections from 78 nodules with diagnosis of follicular tumors were applied to the detection of immunocytochemical staining for minichromosome maintenance protein (MCM2), growth arrest and DNA damage-induced nuclear protein 153 (GADD153), and Ki-67.Results Satisfaction rate of cytological smear combined with cell block specimen was 94.3 ％ (815/864) and accuracy rate of the diagnosis was 94.0％ (766/815), which were higher than in cytological smear group (P＜0.01).The false negative rate of cytological smear combined with cell block specimen was 16.6％ (41/247)in diagnosis of thyroid cancer.Positive rate of M CM2 and GADD153 in thyroid follicular neoplasia were lower than that of follicular carcinoma (P ＜ 0.01).There was no significant difference between thyroid follicular neoplasia and follicular carcinoma in regard to positive rate of Ki-67 (P ＞ 0.05).Conclusions The combination of ultrasound-guided fine needle aspiration-yielded cell block and molecular markers has great significance in early diagnosis of thyroid cancer and differentially diagnosis of thyroid follicular tumor.