Objective To investigate the analgesic effect of different doses of dezocine on a patient-controlled intravenous analgesia(PCIA) for pain control after major abdominal surgery.Methods Sixty patients (ASA Ⅰ orⅡ) undergoing major abdominal surgery were randomly divided into three groups of A,B,and C (n=20).Patients received a dezocine loading dose of 0.12 mg/kg at 20 min before the end of surgery.The background infusion of dezocine is 0.012,0.014 mg·kg1·h1 and 0.016 mg·kg1·h-1 in group A,B,and C,respectively.Visual analogue scores (VAS),Ramsay score,the analgesic consumption,the total number of patient controlled analgesia (PCA),the effective number of PCA,and the side effects (nausea,vomiting,dizziness and respiratory depression) were recorded at 6,12,24,48 h postoperatively.Results At 6,12,24,48 h postoperatively,the VAS scores in group C [(1.8±1.1),(1.5±0.8),(1.3±0.9),(1.1±0.9)] were significantly lower than those of group A[(3.0±1.1),(2.4±0.9),(2.0±0.7),(1.8±0.8)] and B [(2.8±1.0),(2.3±0.6),(1.8±0.8),(1.7±0.7)](P＜0.05).Meanwhile,the Ramsay scores were higher in group C[(2.2±0.6),(2.3±0.6)] than those in group A [(1.7±0.7),(1.8±0.6)] and B[(1.8±0.6),(1.9±0.6)](P＜0.05) at 6 h and 12 h after surpery.The scores of satisfaction of postoperative analgesia,analgesic consumption,the total and effective number of PCA were also lower in group C than the other groups (P＜0.05).Moreover,there is no statstical difference on the incidence of adverse effects among the three groups.Conclusions Patient-controlled intravenous analgesia with 0.016 mg·kg-1·h-1 dezocine shows the best analgesic effect,and the similar incidence of side effects.