ObjectiveTo investigate the changes of serum concentration of parathyroid hormone (PTH) and calcium after thyroid surgery and compare the changes among different modes of operation. MethodsFrom Aug. 2006 to Dec. 2009, 470 patients accepted thyroid surgery. The serum concentration of PTH and calcium in different groups was measured and compared before and 1 day after surgery. According to the extent and similarity of the surgery, patients were classified into 7 groups and they were compared in terms of postoperative changes of PTH and serum calcium. Statistical analysis was performed. ResultsThe serum concentration of PTH and calciurn decreased significantly after surgery in all patients except for those receiving unilateral and bilateral partial thyroidectomy. Compared with unilateral lobectomy, surgeries such as bilateral subtotal thyroidectomy, unilateral thyroidectomy with contralateral subtotal thyroidectomy, bilateral near-total thyroidectomy and total thyroidectomy resulted in more dramatic decreases of serum concentration of PTH and calcium and higher incidence of hypocalcemia ( P ＜ 0.05 ). The comparison between patients receiving CLND or not had the same result. Conclusions Almost all kinds of thyroid surgery affect the parathyroid function. The wider the surgery, the higher the possibility of postoperative hypoparathyroidism. The indications and criteria of different types of thyroid surgery are essential for hypoparathyroidism prevention. In some cases, vitamin D and calcium are recommended for preventive purpose.