ObjectiveTo compare effects of warm water infusion and air insufflation on patient tolerance and satisfaction during the insertion phase of unsedated colonoscopy. MethodsIn a single-center， prospective， single blind randomized trial， patients were randomly assigned to three groups （water infusion group， air insufflation group， or hybrid method group） during the insertion phase of colonoscopy. Main outcome measurements included insertion time， cecal intubation rate， adenoma detection rate， the rate of position change， the rate of abdominal compression， intraoperative pain and distension VAS scores， postoperative pain and distension VAS scores. ResultsA total of 180 cases were enrolled， 60 in each group. Patients in water infusion group and hybrid method group required less abdominal compression or position change， longer insertion time， reported lower intraoperative pain and distension VAS scores than air insufflation group during the insertion phase of colonoscopy. There were no significant differences in cecal intubation rates， adenoma detection rates， postoperative pain and distension or VAS scores among three groups. ConclusionWater infusion significantly decreases patient abdominal pain and distension during the insertion phase of colonoscopy without affecting cecal intubation rate and adenoma detection rate.