Objective To explor the safty and the effect of controlled intravenous analgesia with remifentanil on hyoxemia in obese patients with painless gastroscopy.Methods One hundred patients undergoing painless gastroscopy were randomly and equally allocated into 2 groups(50 each).In group R,anesthesia was induced with TCI(target-controlled infusion) of remifentanil,and the target plasma concentration (Cp) of propofol was set at 2ng/ml.In group N,the same volume of saline was continues infusion.MAP,RR and HR were monitored and recorded before the examination(T0),the time point of examination start(T1),gastroscopy go through glottis(T2),at the end of the operation (T3) and 5 min after examination (T4).The effect of sedation was evaluated by Ramsay.Except that,gastroscopy time,the satisfaction of patient,anesthetist and endoscopist were recored.In addition,apnea,bradycardia,hypoxemia,myoclonus,body movement,hypotension and postoperative complications were also recorded.Results Compared with group N,in group R,HR,MAP and rate of body movement were significantly decreased (P ＜ 0.05).Except that,the satisfaction of patient and endoscopist were increased (P ＜ 0.05).Conclusion TCI of remifentanil can provide satisfaction sedation for obese patients with painless gastroscopy with few adverse effects.