Objective: To study the clinical significance of serum calcitonin in the diagnosis and treatment of medullary thyroid carcinoma and to analyze its cost-benefit. Methods: One hundred and forty one patients with medullary thyroid carcinoma who undertook calcitonin test and frozen pathological examination were enrolled in this study from Oct 2012 to Mar 2018. Using the method of χ² test, the positive rate of calcitonin test and frozen pathological examination in diagnosis of medullary thyroid carcinoma(MTC) were compared. Firstly, we compared the correct checkout cost of calcitonin test and that of frozen pathological examination (total number of patients×cost of examination/the correctly detected number of patients) . Secondly, we calculated whether calcitonin test help patients save money(average cost of treatment in hospital for MTC×number of patients who were evaluated to be candidate for surgery-cost of calcitonin test×total number of patients)/total number of patients. Results: 139 patients were positive in calcitonin test among 141 patients, and the positive rate was 98.58%. 91 patients were positive in frozen pathological examination, and the positive rate was 64.54% (χ²=97.821, P<0.000 1) . Cost-benefit analysis showed that the correct checkout cost of calcitonin test and frozen pathological examination were 71.01 yuan and 426.10 yuan, also,1 371 938.64 yuan could be saved totally and 9 730.06 yuan could be saved per patient because of calcitonin test. Conclusion Serum calcitonin test had a significant effect on the diagnosis and treatment of medullary thyroid carcinoma and was economical and practical.