Objective To investigate the effects of postoperative melatonin on the postoperative sleeping in patients undergoing laparoscopic total hysterectomy under general anesthesia and possible underlying mechanisms. Methods A total of 120 patients who were scheduled for laparoscopic total hysterectomy under general anesthesia were enrolled. According to the random number table method, the patients were assigned to three groups (n=40): a 5 mg melatonin group (group A), a 10 mg melatonin group (group B) and a placebo group (group C). Patients in groups A, B, and C were administered with 5 mg melatonin, 10 mg melatonin and a placebo with the same shape, taste and smell after collection of saliva on the surgery day, Day 1 after surgery and Day 2 after surgery. The saliva was collected from patients at 21:00 on the day before surgery, the surgery day, Day 1 after surgery and Day 2 after surgery. The levels of salivary cortisol and melatonin were measured by enzyme‑linked immunosorbent assay (ELISA). The Pittsburgh Sleep Quality Index (PSQI) was used to evaluate the incidence of preoperative and postoperative sleep disorders one day before surgery and Day 7 after surgery. The Identity Consequence Fatigue Scale (ICFS‑10) was used to evaluate patient fatigue one day before surgery and Day 7 after surgery. The quality of sleep per night from two days before surgery to Day 2 after surgery was assessed using the St.Mary's Hospital Sleep Questionnaire (SMH). The duration of operation, dosage of anesthetics and the use of rescue analgesics, the incidence of complications within 48 h after surgery were recorded. The Numerical Rating Scale (NRS) pain scores were recorded one day before surgery, during extubation, the surgery day, Days 1‒3 after surgery, and Day 7 after surgery. Results The incidence of postoperative sleep disturbance in groups A, B and C was 44.7%, 23.7% and 65.8%, respectively, where group B presented remarkable decreases compared with group C (P<0.01). The SMH score of groups A and B was significantly higher than that of group C on the surgery day and Day 1 after surgery (P<0.01), and the SMH score of group B was significantly higher than that of group A Day 1 after surgery (P<0.05). Compared with group C, the content of salivary melatonin in groups A and B significantly increased on Days 1 and after surgery (P<0.05). After surgery, the ICFS‑10 score of group B was significantly lower than of group C (P<0.01). The postoperative salivary cortisol level in the three groups was significantly higher than those before operation (P<0.01), and there was no significant difference between the groups at the same time point. There was no significant difference in other indexes (P>0.05). Conclusions Oral administration of 10 mg melatonin for three consecutive days after laparoscopic total hysterectomy under general anesthesia can reduce the incidence of postoperative sleep disorders. Oral administration of 5 mg melatonin can improve patients' sleep quality at night, while 10 mg melatonin produced better improvement in patient sleep quality better than 5 mg melatonin.