Objective: To investigate the effects of preoperative quetiapine on postoperative delirium (POD) and sleep quality in elderly orthopedic patients. Methods: Prospectively, 111 elderly patients, American Society of Anesthesiologists (ASA) grade Ⅱ-Ⅲ, scheduled to undergo knee or hip surgery in the Affiliated Huangyan Hospital of Wenzhou Medical University under continuous spinal anesthesia from August 2021 to March 2023, were selected and randomly divided into two groups by random number table: control group (group C, 1 h preoperative placebo) and quetiapine group (group Q, 1 h preoperative quetiapine 12.5 mg). In group C, 54 cases were enrolled, including 25 males and 29 females, with an average age of (73.5±4.9) years. In group Q, 57 cases were enrolled, including 26 males and 31 females, with an average age of (74.8±5.0) years. The primary outcome measures were the incidence of POD evaluated by using confusion assessment method (CAM) at 24, 48, and 72 hours after surgery, and the secondary outcome measures included Pittsburgh sleep quality index (PSQI) scores at 24 and 48 hours after surgery and satisfaction of pain management within 24 hours after surgery. Results: The incidence of POD at 24, 48, and 72 h after surgery in group Q was 5.4% (3/57), 12.5% (7/57), 14.3% (8/57), respectively, while that in group C was 18.2% (10/54), 21.8% (12/54), 21.8% (12/54), respectively. The incidence of POD at 24 h after surgery in group Q was lower than that in group C (P=0.036). There was no significant difference in the incidence of POD at 48 and 72 h after surgery between two groups (all P>0.05). The PSQI score of patients in group Q at 24 and 48 h after surgery were (3.8±1.2) and (6.9±1.1) scores, respectively, which in group C were (10.5±2.8) and (7.3±1.3) scores, respectively. Compared with group C, the PSQI score of patients in group Q at 24 h after surgery was significantly higher (P<0.001), but there was no significant difference at 48 h after surgery (P=0.068). The satisfaction scores of pain management at 24 h after surgery in group Q was (91±7) scores, which was higher than that in group C of (81±6) scores (P<0.001). Conclusion: Oral intake of low-dose quetiapine 1 h preoperatively can reduce the incidence of POD, improve postoperative sleep quality and enhance postoperative satisfaction of pain management at 24 hours after surgery in elderly orthopedic patients undergoing knee or hip surgery.