OBJECTIVE The purpose of this study was to evaluate the efficacy of 360-degree suture trabeculotomy (360S-LOT) ab interno for treating open-angle glaucoma (OAG). Risk factors of surgical failure were examined. METHODS 360S-LOT ab interno alone was performed for patients with uncontrolled OAG, and combined 360S-LOT ab interno/phacoemulsification was performed for patients with controlled OAG with a visually significant cataract between March 2014 and September 2015 at a single center. The patients were prospectively followed for 2 years. The main outcome measures included 2-year intraocular pressure (IOP), number of anti-glaucoma medications used, postoperative complications, and predictive factors of surgical failure. Kaplan-Meier analysis was performed, with surgical success (with or without medication use) defined as postoperative IOP ≤15 mmHg and IOP reduction ≥20% (criterion A) or IOP ≤12 mmHg and IOP reduction ≥30% (criterion B). Predictive factors were evaluated using Cox proportional hazard ratios. RESULTS A total of 64 eyes of 64 patients were included, and 50 (78%) eyes of 64 eyes underwent a phacoemulsification combination procedure. Surgery significantly reduced IOP from 18.4 ± 2.9 mmHg before surgery to 13.4 ± 3.0 mmHg after surgery (P < 0.001). Patients used an average of 1.8 ± 1.5 medications before surgery and 1.3 ± 1.5 medications after surgery (P = 0.101). No serious postoperative complications were observed. The probability of surgical success was 49.2% and 16.0% using criteria A and B, respectively. No risk factors of surgical failure were identified. CONCLUSIONS The 360S-LOT ab interno procedure is a favorable option for treating eyes with mild or moderate OAG.