Objective To evaluate the usefulness of the thyroglobulin(Tg) level in adults as a nutritional biomarker of iodine status and to identify the factors related to the serum Tg level. Methods A cross-sectional study was conducted in adult populations of areas differing in iodine nutrition from three provinces(Autonomous Region) in China. Serum levels of thyroid hormones and Tg as well as thyroid autoantibodies were measured. The thyroid volume and nodule were measured by ultrasound. A multivariate linear regression analysis was used to assess iodine intake and other indeterminate factors associated with the serum Tg level. Results A total of 573 adults were recruited for this study. The serum Tg levels differed significantly among the three groups(22.27 μg/L, 9.73 μg/L and 15.77 μg/L in the excess, more-than-adequate, and deficient groups, respectively). The results of multivariate linear regression analysis indicate that excess and deficient iodine intake, goiter, thyroid nodule, hypothyroidism are significantly related with higher Tg level, and Tg Ab positivity is significantly related with lower serum Tg. Conclusion The serum Tg level reflects abnormal thyroid function and is a sensitive functional biomarker of iodine nutrition status. Objective To evaluate the usefulness of the thyroglobulin (Tg) level in adults as a nutritional biomarker of iodine status and to identify the factors related to the serum Tg level. Methods A cross-sectional study was conducted in adult populations of areas differing in iodine nutrition Thumroid levels of thyroid hormones and Tg as well as thyroid autoantibodies were measured. The thyroid volume and nodule were measured by ultrasound. A multivariate linear regression analysis was used to assess iodine intake and other indeterminate factors associated with the serum Tg level. Results A total of 573 adults were recruited for this study. The serum Tg levels differed significantly among the three groups (22.27 μg / L, 9.73 μg / L and 15.77 μg / L in the excess, more- than-adequate, and deficient groups, respectively). The results of multivariate linear regression analysis indicate that excess and deficient iodine intake, goiter, thyroid nodule, hypo Thyroidism are significantly related with higher Tg level, and Tg Ab positivity is significantly related with lower serum Tg. Conclusion The serum Tg level determines the abnormal thyroid function and is a sensitive functional biomarker of iodine nutrition status.