Background/aims This study was to explore the 1-year interim efficacy and safety of canaloplasty for primary open-angle glaucoma (POAG) with failed glaucoma filtration surgery (GFS) but an intact Schlemm's canal (SC). Methods This was a single-surgeon prospective clinical study. Patients with POAG scheduled for canaloplasty were included and divided into two groups (with or without failed GFS). The status of SC was determined by gonioscopy and ultrasound biomicroscopy. Primary outcome measures included intraocular pressure (IOP) and glaucoma medication use at various follow-up points. The secondary outcome measure was the rate of surgical success. Results Thirty-seven eyes were enrolled in group 1 (no GFS) and 23 eyes were enrolled in group 2 (failed GFS). The mean IOP (16.0 +/- 1.6 vs 16.2 +/- 1.6 mm Hg) and the number of medications (0.3 +/- 0.8 vs 0.3 +/- 0.6) at 18 months after canaloplasty were not significantly different between the two groups. There was no significant difference in complete success rate (criteria A: 52.2% vs 59.5%, p=0.587; criteria B: 39.1% vs 48.6%, p=0.343), as well as the qualified success rate (criteria A: 86.5% vs 82.6%, p=0.668; criteria B: 78.4% vs 69.6%, p=0.445). In group 2, the age, sex, number of previous surgeries, time span between operations were not significantly associated with surgery failure (p=0.199, 0.747, 0.977 and 0.615). Hyphaema was the most common postoperative complications. Conclusions Canaloplasty is an effective and safe option for POAG with failed GFS but an intact SC.