Abstract： Background::Ciprofol (HSK3486; Haisco Pharmaceutical Group Co., Ltd., Chengdu, China), developed as a novel 2,6-disubstituted phenol derivative showed similar tolerability and efficacy characteristics as propofol when applicated as continuous intravenous infusion for 12 h maintenance sedation in a previous phase 1 trial. The phase 2 trial was designed to investigate the safety, efficacy, and pharmacokinetic characteristics of ciprofol for sedation of patients undergoing mechanical ventilation.Methods::In this multicenter, open label, randomized, propofol positive-controlled, phase 2 trial, 39 Chinese intensive care unit patients receiving mechanical ventilation were enrolled and randomly assigned to a ciprofol or propofol group in a 2:1 ratio. The ciprofol infusion was started with a loading infusion of 0.1-0.2 mg/kg for 0.5-5.0 min, followed by an initial maintenance infusion rate of 0.30 mg·kg -1·h -1, which could be adjusted to an infusion rate of 0.06 to 0.80 mg·kg -1·h -1, whereas for propofol the loading infusion dose was 0.5-1.0 mg/kg for 0.5-5.0 min, followed by an initial maintenance infusion rate of 1.50 mg·kg -1·h -1, which could be adjusted to 0.30-4.00 mg·kg -1·h -1 to achieve -2 to +1 Richmond Agitation-Sedation Scale sedation within 6-24 h of drug administration. Results::Of the 39 enrolled patients, 36 completed the trial. The median (min, max) of the average time to sedation compliance values for ciprofol and propofol were 60.0 (52.6, 60.0) min and 60.0 (55.2, 60.0) min, with median difference of 0.00 (95% confidence interval: 0.00, 0.00). In total, 29 (74.4%) patients comprising 18 (69.2%) in the ciprofol and 11 (84.6%) in the propofol group experienced 86 treatment emergent adverse events (TEAEs), the majority being of severity grade 1 or 2. Drug- and sedation-related TEAEs were hypotension (7.7% vs. 23.1%, P = 0.310) and sinus bradycardia (3.8% vs. 7.7%, P = 1.000) in the ciprofol and propofol groups, respectively. The plasma concentration-time curves for ciprofol and propofol were similar. Conclusions::ciprofol is comparable to propofol with good tolerance and efficacy for sedation of Chinese intensive care unit patients undergoing mechanical ventilation in the present study setting.Trial registration::ClinicalTrials.gov, NCT04147416.