AIM: To evaluate the safety and efficacy of posterior scleral application (a modified technique) of an antimetabolite mitomycin C-soaked sponge in trabeculectomy for patients with glaucoma. METHODS: This retrospective study included 101 patients (115 eyes) with glaucoma (aged 12–83y) who underwent trabeculectomy using a modified mitomycin C-soaked sponge placement method. A piece of 3.5×10 mm2 sponge was placed vertically and posteriorly with the long side perpendicular to the limbus. The mitomycin C concentration and exposure time were 0.2–0.5 mg/mL and 1–5min, respectively. Intraocular pressure, best-corrected visual acuity, and hypotensive medications were recorded at baseline and at the final visit. Complications, interventions required, and bleb morphology were recorded postoperatively. The primary outcome was trabeculectomy safety, including complications and bleb morphology; the secondary outcome was the trabeculectomy success rate. RESULTS: At the final follow-up [median 28mo, range 7–67mo and interquartile range (IQR) 13mo], the qualified (cumulative) success rate was 93.0% and the complete success rate was 60.0%. No bleb-related complications were observed. The mean height, extent, and vascularity grades were 0.6±0.9, 1.1±0.4, and 2.4±0.9, respectively. All Seidel tests were negative. The mean posteriority grade was 0.8±0.4. CONCLUSION: Trabeculectomy with the long side of a mitomycin C-soaked sponge placed perpendicular to the corneal limbus is safe and effective.