Background The Forrest classification is widely applied to guide endoscopic hemostasis for peptic ulcer bleeding. Accordingly, practice guidelines suggest medical treatment only for ulcer with a Forrest IIc lesion because it has low rebleeding risk even without endoscopic therapy, ranging from 0 to 13%. However, the risk ranges widely and it is unclear who is at risk of rebleeding with such a lesion. This study assessed whether the Rockall score, which evaluates patients holistically, could indicate the risk of recurrent bleeding among patients with a Forrest IIc lesion at the second-look endoscopy. Methods Patients who had peptic ulcer bleeding with Ia-IIb lesions received endoscopic hemostasis at the primary endoscopy, and they were enrolled if their Ia-IIb lesions had been fading to IIc at the second-look endoscopy after 48- to 72-h intravenous proton pump inhibitor (PPI) infusion. Primary outcomes were rebleeding during the 4th–14th day and 4 th –28th day after the first bleeding episode. Results The prospective cohort study enrolled 140 patients, who were divided into a Rockall scores ≥ 6 group or a Rockall scores < 6 group. The rebleeding rates in the Rockall scores ≥ 6 group and the Rockall scores < 6 group during the 4th–14th day and the 4th–28th day were 13/70 (18.6%) versus 2/70 (2.9%), p  = 0.003 and 17/70 (24.3%) versus 3/70 (4.3%), p  = 0.001, respectively, based on an intention-to-treat analysis and 5/62 (8.1%) versus 0/68 (0%), p  = 0.023 and 6/59 (10.2%) versus 0/67 (0%), p  = 0.009, respectively, based on a per-protocol analysis. The Kaplan–Meier curves showed that the Rockall scores ≥ 6 group had a significantly lower cumulative rebleeding-free proportion than the Rockall scores < 6 group ( p  = 0.01). Conclusions Combined Rockall scores ≥ 6 on arrival with a Forrest IIc lesion at the second-look endoscopy can identify patients at risk of recurrent peptic ulcer bleeding following initial endoscopic and intravenous PPI treatment. Trial registration Trial registration identifier: NCT01591083