Background <p>This study aimed to investigate the effects of dexamethasone on blood glucose in diabetic patients undergoing thoracoscopic surgery, providing a reference for its safe intraoperative use in this population.</p> Methods <p>In this randomized, double-blind controlled trial, 60 diabetic patients with reasonably controlled blood glucose (HbA1c &lt; 9%) for thoracoscopic surgery were randomly assigned (1:1) to the experimental group (intravenous dexamethasone 10&#xa0;mg/2&#xa0;mL) or the control group (the same volume of normal saline). Blood glucose measurements were taken at 2 h (h) and 4 h post-administration, and on postoperative days (POD) 1, 2, and 3. we calculated the incidence of postoperative hyperglycemia and the number of patients requiring additional insulin; postoperative visual analogue scale(VAS) pain scores and postoperative nausea and vomiting(PONV) incidence; chest tube removal time, and postoperative hospital stay, incidence of adverse events, 90-day readmission and mortality rates.</p> Results <p>Compared with preoperative levels, blood glucose increased at 2 h and 4 h after administration in both groups (both <i>P</i> &lt; 0.05) and returned to baseline by POD 1 (both <i>P</i> &gt; 0.05). Compared with the control group, the experimental group showed higher blood glucose at 2 h and 4 h post-administration (<i>P</i> &lt; 0.05), but there were no significant differences between groups on postoperative days(POD)1, 2, and 3 (<i>P</i> &gt; 0.05). The incidence of hyperglycemia (all time points) and additional insulin use showed no significant differences between groups (<i>P</i> &gt; 0.05). The experimental group had lower VAS pain scores at 2 h postoperatively and on POD 1, 2, and 3 (P &lt; 0.05) and lower PONV incidence on postoperative day 1 (P &lt; 0.05). PACU hypoxemia occurred in 3.3% of the experimental group and 16.7% of the control group (<i>P</i> = 0.195). The median time to chest tube removal was 1 day shorter in the experimental group compared with the control group (<i>P</i> = 0.018). Median hospital stay was 4 days in the experimental group and 5 days in the control group (<i>P</i> = 0.073). The incidence of adverse events such as pulmonary infection and delayed wound healing, as well as 90-day readmission and mortality rates, showed no significant differences between groups (all <i>P</i> &gt; 0.05).</p> Conclusion <p>Dexamethasone can be safely used in diabetic patients with reasonably controlled blood glucose (HbA1c &lt; 9%) undergoing thoracoscopic surgery and the drug can effectively improve postoperative recovery.</p>