Objective:To investigate the relationship between hypocalcemia and parathyroid hormone(PTH) level during thyroidectomy,and discuss the prevention and treatment of hypocalcemia after thyroidectomy. Methods:The clinical data of 592 cases performed thyroidectomy bdtween January 2004 and August 2007 were analyzed and serum calcium level was observed closely.PTH was checked before,during and after the operation. Results:Hypocalcemia occurred in 86 cases during the postoperative period.The morbidity of hypocalcemia of the patients with serum PTH level less than 15 ng/L (10 minutes after the thyroidectomy) was 1419%,which was significant different with that of patients with serum PTH level more than 15 ng/L (0.34%).The morbidity of hypocalcemia of the patients with serum PTH level less than 10 ng/L(1 day after the operation) was 8.28%,which was significant different with that of patients with,serum PTH level more than 10 ng/L(6.25%).The PTH level reduced more than 75% 10 min after the ectomy was a predictor of hypocalcemia with the sensitivity and specificity of 100% and 9451%. Conclusion:The PTH level reduced more than 75% 10 min after the ectomy,as a predictor,was reliable.The serum calcium level changed significantly within the first 3 days after the operation.The PTH level should be observed during the operation for the patients accepted unilateral lobectomy with contralateral subtotal lobectomy or even larger lobectomy,Which is useful for preventing hypocalcemia.