Abstract: Objective To observe the effect of dizocine combined with propofol on respiratory depression in obese patients undergoing painless colonoscopy. Methods A total of 92 obese patients were randomly divided into two groups: a dizocine group (Group D) and a control group (Group C). They were administered with 0.05 mg/kg dizocine (diluted to 5 ml) or 5 ml normal saline, before intravenous injection of 2 mg/kg propofol 5 min later. Propofol was pumped at 4 mg· kg^-1· h^-1 for anesthesia maintenance. The primary outcomes were the number of times oxygen saturation(SpO₂) decreased. The secondary outcomes were the number of apnea episodes, the time of the first hypoxia episode and the total consumption of propofol. Meanwhile, unconsciousness time, the time of recovery, postoperative Ramsay score, the length of post-anesthesia care unit (PACU) stay, VAS score, endoscopist and patient satisfaction and adverse events like respiratory recycle inhibition were observed. Results There were no statistical difference in demographic characteristics between the two groups. Compared with group C, group D showed decreases in the number of apnea episodes, the number of times SpO₂ decreased, the amount of propofol used, the time of unconsciousness and the time of recovery, the length of PACU stay, and VAS scores, as well as improvement in endoscopist and patient satisfaction (P<0.05 orP<0.01). According to the Kaplan-Meier curve, the median time of the first hypoxia attack in group D (71.5 s) was significantly longer than that in group C (53.5 s) (P<0.01). There was no significant difference in Ramsay score and adverse event rate between the two groups (P>0.05).Conclusions The combined use of dezocine and propofol for painless colonoscopy can reduce the number of times SpO₂ declines and apnea in obese patients, and improve the safety of anesthesia.