Background and study aims It remains unclear whether the experience of endoscopists affects clinical outcomes for acute lower gastrointestinal bleeding (ALGIB). We aimed to determine the feasibility and safety of colonoscopies performed by nonexperts using secondary data from a randomized controlled trial for ALGIB. Patients and methods We analyzed clinical outcomes in 159 patients with ALGIB who underwent colonoscopies performed by two groups of endoscopists: experts and nonexperts. We compared endoscopy outcomes, including identification of stigmata of recent hemorrhage (SRH), successful endoscopic treatment, adverse events (AEs), and clinical outcomes between the two groups, including 30-day rebleeding, transfusion, length of stay, thrombotic events, and 30-day mortality. Results Expert endoscopists alone performed colonoscopies in 96 patients, and nonexperts performed colonoscopies in 63 patients. The use of antiplatelets and warfarin was significantly higher in the expert group. The SRH identification rate (24.0 and 17.5 %), successful endoscopic treatment rate (95.0 and 100 %), rate of AEs during colonoscopy (0 and 0 %), transfusion rate (6.3 and 4.8 %), length of stay (8.0 and 6.4 days), rate of thrombotic events (0 and 1.8 %), and mortality (0 and 0 %) were not different between the expert and nonexpert groups. Rebleeding within 30 days occurred more often in the expert group than in the nonexpert group (14.3 vs. 5.4 % P = 0.0914). Conclusions The performance of colonoscopies for ALGIB by nonexperts did not result in worse clinical outcomes, suggesting that its use could be feasible for nonexperts for diagnosis and treatment of ALGIB.