Patients with membranous nephropathy (MN) and poor kidney function or active disease despite previous immunosuppression are underrepresented in clinical trials. It is unknown how effective rituximab is in this population. This prospective, multi-centre, single-arm, real-world study of patients with active MN [urine protein-creatinine ratio (uPCR) >350mg/mmol and serum albumin <30g/L, or a fall in estimated glomerular filtration rate (eGFR) of at least 20% or more over at least 3months] evaluated rituximab in those with contraindications to calcineurin inhibitors and cytotoxic therapy. The primary outcome was change in rate of eGFR decline before and after rituximab. Complete or partial remission were defined as uPCR <30mg/mmol or uPCR <350mg/mmol with a ≥50% fall from baseline, respectively. A total of 180 patients [median age 59years, interquartile range (IQR) 48-68] received rituximab and were followed up for a median duration of 17months. Seventy-seven percent had prior immunosuppression. Median eGFR and uPCR at baseline were 49.2mL/min/1.73m2 (IQR 34.4-80.6) and 766mg/mmol (IQR 487-1057), respectively. The annual rate of decline of eGFR fell from 13.9 to 1.7mL/min/1.73m2/year following rituximab (Z score=2.48, P<.0066). At 18months 12% and 42% of patients were in complete or partial remission, respectively. Rituximab was well tolerated; patient survival was 95.6% at 2years and in patients in whom eGFR was available, kidney survival was 93% at 2years. Rituximab significantly reduced the rate of eGFR decline in active MN including those who had received prior immunosuppression or with poor baseline kidney function.