Ｏｂｊｅｃｔｉｖｅ　To observe the effect of oxycodone for inhibition of myoclonus induced by etomidate during the induction of general anesthesia in middle-aged or elderly patients.　Methods　Sixty-two cases of patients undergoing elective general anesthesia, ASA Ⅰor Ⅱ grade, were assigned into middle aged group (45 to 54 years old) 30 cases, and aged group (65 to 74 years old) 32 cases. Induction of anesthesia: with oxygen mask(8 L/min) for five minutes, all patients were injected oxycodone intravenously in thirty seconds with modified sequential method. Two minutes later, all were injected etomidate 0.3 mg/kg intravenously in thirty seconds. Then, we assessed the occurrence and degree of myoclonus for two minutes continuously. After that, we administrated cisatracurium 2 mg/kg and fentanyl 3 μg/kg. We completed the mechanical ventilation with tracheal intubation in five minutes. Anesthesia was maintained with propofol（3.0 mg/L）and remifentanil(2.5~3.0 μg/L) in target controlled infusion(TCI) mode until the end of surgery. ED50 and 95%CI of oxycodone during the induction of general anesthesia were calculated. The total time of operation, extubation time and adverse effects such as nausea and vomiting were also recorded.　Results　ED50 of the middle-aged group and elderly group was 0.077 mg/kg and 0.062 mg/kg, and 95%CI of the two groups was 0.045-0.122 mg/kg and 0.043~0.101 mg/kg respectively. The dose of oxycodone used in middle-aged group was significantly higher than that in elderly patients group(P<0.05). There was no significant difference of adverse reaction between the two groups(P>0.05).　Conclusions　The ED50 and 95%CI of oxycodone for inhibition of myoclonus induced by etomidate during the induction of general anesthesia in middle-aged or elderly patients are 0.077 mg/kg and 0.062 mg/kg, 0.045-0.122 mg/kg and 0.043-0.101 mg/kg respectively.