Background and purpose: Dexamethasone is known to produce analgesic effects, but the optimal analgesic dosage of dexamethasone remains unclear, especially in patients without postoperative use of other analgesics. The purpose of this study was to explore the effective analgesic dose of dexamethasone in day surgery patients undergoing painless abortion. Methods: 287 patients undergoing painless abortion were randomly assigned to one of four groups: control group receiving saline and dexamethasone groups receiving 0.1, 0.15, or 0. 2 mg/kg dexamethasone. Drugs were intravenously injected 30 min before induction of anesthesia. All patients underwent the same anesthesia procedure using propofol and remifentan. The visual analogue scale (VAS) scores and occurrence of nausea, vomiting and drug-induced side effects were recorded at 1, 2 and 24 h after operation. Results: There were no significant differences in patient's clinical characteristics, surgical features and frequency of occurrence of nausea and vomiting among the four groups (P > 0.05). The VAS scores at rest and during coughing at 2 h after operation (time of discharge from the hospital) were significantly lower in patients receiving 0.2 mg/kg dexamethasone compared with control patients (P < 0.05). Conclusion: Intravenous injection of 0.2 mg/kg dexamethasone before induction of anesthesia can significantly reduce the VAS scores at 2 h after painless abortion.