The occurrence of significant pain and paresthesia after robot-assisted transaxillary thyroidectomy has been reported, and some patients experience chronic symptoms even three months after surgery. This study scrutinized the effects of deep neuromuscular block during robot-assisted transaxillary thyroidectomy on postoperative pain and sensory changes. In this single-blinded, prospective, randomized, controlled trial, 88 patients who underwent robot-assisted transaxillary thyroidectomy were enrolled and randomly allocated to either the moderate or deep neuromuscular block groups. Study endpoints included postoperative pain, paresthesia, and sensory change after surgery. The linear mixed models for numeric rating scale pain scores in the chest, neck, and axilla all showed significant intergroup differences over time (p = 0.003 in chest; p = 0.001 in neck; p = 0.002 in axilla). In the post hoc analysis with Bonferroni correction, the pain scores of the chest, neck, and axilla were significantly lower in the deep neuromuscular block group on postoperative day one compared to the moderate neuromuscular block group (adjusted p < 0.001 in chest, neck, and axilla). This study demonstrated that deep neuromuscular block could reduce postoperative pain after robot-assisted transaxillary thyroidectomy. However, it could not demonstrate that deep neuromuscular block reduces paresthesia or hypoesthesia after the surgery.