Previous studies have demonstrated that terminal fucosylation is associated with the biological aggressiveness of carcinomas, but the significance of core fucosylation (alpha1,6-fucosylation) through alpha1,6-fucosyltransferase (FUT8) has not been studied in depth. Herein, we investigated the expression of alpha1,6-fucosyltransferase (FUT8) in 133 cases of thyroid carcinomas using an immunohistochemical approach. The expression of FUT8 was quite low in normal follicules. A high expression of FUT8 was observed in 33.3% of papillary carcinoma and the incidence was directly linked to tumor size and lymph node metastasis. In contrast, this phenomenon was less frequently observed in follicular carcinoma and anaplastic (undifferentiated) carcinoma. These results suggest that FUT8 expression may be a key factor in the progression of thyroid papillary carcinomas, but not follicular carcinomas, and decreases in FUT8 expression might be linked to anaplastic transformation.