Abstract: Objective To determine the maximum dose of continuously infused mivacurium for intraoperative neuromonitoring and observe its adverse effects in thyroid surgery. Methods Twenty-eight patients undergoing thyroid surgery with intraoperative neuromonitoring received continuous infusion of mivacurium at the initial rate of 5.43 μg·kg-1 ·min-1, and the infusion rate for the next patient was adjusted based on the response of the previous patient according to the results of neurological monitoring. The depth of anesthesia was maintained with sevoflurane and remifentanil during the surgery. The LD50 and 95%CI of mivacurium were calculated using Brownlee’s up-and-down sequential method. Results The LD50 of continuously infused mivacurium was 8.94 μg·kg-1·min-1 (95% CI: 8.89- 8.99 μg·kg-1·min-1) during thyroid surgery, which did not affect neurological function monitoring. Transient chest skin redness occurred after induction in 9 patients (32.1%). None of the patients experienced intubation difficulties or showed intraoperative body motions during the surgery. Conclusion In patients undergoing thyroid surgery under anesthesia maintained by inhalation and intravenous infusion, the LD50 of mivacurium was 8.94 μg·kg-1 ·min-1 (95% CI: 8.89-8.99 μg·kg-1 ·min-1) for continuous infusion, which does not cause serious adverse effects during the operation.