Objective: To investigate the clinical features and outcome of hydronephrosis induced by retroperitoneal fibrosis (RPF), and to evaluate the effect of corticosteroid based therapy combined with surgical intervention of ureteral obstruction. Methods: A total of 17 RPF patients with hydronephrosis hospitalized in Peking University International Hospital from May 2016 to December 2019 were analyzed retrospectively. Results: The median age was 56 (53, 65) years, the male to female ratio was 2.4:1, and the disease duration was 4.00 (0.83, 8.00) months. The initial symptoms included back pain (9 cases), abdominal pain (6 cases), oliguria (2 cases) and lower limb edema (3 cases). Eight patients presented left hydronephrosis, 1 right hydronephrosis and 8 bilateral hydronephrosis. C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) were both elevated in 13 patients (76.5%, n=17). Immunoglobin (Ig) G4 increased in 5 cases (29.4%, n=17). IgG, IgE and IgA increased in 4 cases (30.8%, n=13), 4 cases (30.8%, n=13) and 1 case (7.7%, n=13), respectively. Among 12 patients who underwent biopsy, 3 patients were diagnosed with IgG4-relate disease. The level of IgG4 in the tissues varied, 6 cases expressed less than 10 per high power field (HPF) or no expression (50.0%). Only 2 cases expressed 10-30/HPF (16.7%), and 4 cases revealed more than 30/HPF (33.3%). Among the 17 patients with ureteral obstruction, no urinary drainage procedure was needed in 4 patients who had mild ureteral obstruction, whereas, ureteral stenting was carried out in the other 13 cases before drug treatment. Time was too short to evaluate the effect of urinary drainage procedures in 4 patients. For the rest, ureterolysis had to be performed in 3 cases after failed ureteral stent insertion. Successful drain removal was accomplished in all of these 9 patients and the mean time to drain removal was (6.7±3.0) months. In addition, 10 patients had complete medical records after an average follow-up time of 5 (3-13) months. Levels of ESR, CRP, IgG4, IgG, IgE, IgA were 54.0 (36.3, 98.5) mm/h, 26.8 (8.7, 53.0) mg/L, 1.34 (0.55, 3.36) g/L, 16.3 (13.0, 21.1) g/L, 40.5 (31.4, 203.0) IU/mL, 2.51 (1.82, 3.25) g/L at baseline, which all decreased predominantly after treatment. ESR, CRP, IgG4, IgG, IgE and IgA dropped by 38.5 (23.5, 54.3) mm/h (P<0.01), 23.0 (5.5, 52.0) mg/L (P<0.05), 0.92 (0.40, 2.85) g/L (P<0.01), 6.5 (1.7, 9.1) g/L (P<0.05), 23.7 (4.8, 162.0) IU/mL (P<0.05) and 0.77 (0.32, 1.26) g/L (P<0.05), respectively. Size of mass measured by CT/MRI imaging became smaller significantly and hydronephrosis relieved. Conclusion: Onset of RPF is insidious and lack of specific initial symptoms. Corticosteroid based therapy combined with surgical intervention of relieving obstruction is effective.