【Abstract】Objective To observe the efficacy of oxycodone under no background doses in patient-controlled intravenous analgesia after Caesarean section. Methods Sixty patients undergoing elective cesarean section were randomized into two groups using random schedual table (n=30): group Morphine (group M) and group oxycodone(group O), all patients were aged between 20 to 35 years and of ASA class I~II. Fifty milligrams of morphine was delivered in group M, while 50 mg oxycodone was delivered in group O. Ondansetron 8 mg was added to each group. PCIA was set on demand mode without loading dose or background infusion. In both groups, drugs were diluted to 100 ml with normal saline(NS), and 4 ml bolus dose with 5 min lockout interval was set. At 4, 8, 12and 48 h after surgery, visual analogue score (VAS) was assessed, including VAS at rest, VAS at motion and VAS at uterine contraction.Total doses of the drug delivery within postoperative 48 h were recorded, and postoperative nausea and vomiting and patient satisfaction were also evaluated. Result At 4, 8, 12 and 24 h after surgery, VAS at uterine contraction in group O was significantly lower than group M(P<0.05). No significant differences were detected between the two groups in VAS at rest and motion at all time points. At 48 h after surgery, total doses of PCIA drugs and the incidences of side effects were significantly lower in group O than in group M(P<0.05). The overall patient satisfaction degree was significantly higher in Group O(P<0.05). Conclusion Both oxycodone and morphine are effective for pain relief after cesarean section when PCIA is set on bolus mode. However, compared with morphine, oxycodone exhibited significantly better effects on uterine contraction pain relief and patient satisfaction.