Background: Membranous glomerulonephritis (MGN) is caused by unknown etiology (idiopathic) or associated with various diseases (secondary). There is no report about etiologic diseases of MGN in Korea, Methods: To determine etiologic diseases of MGN, 29patients (male 24, female 5, mean age 36.4 year) with MGN after renal biopsy were further examined for associated diseases prospectively and their diseases were analyzed by literally, and their clinical and laboratory findings were also evaluated. Results: Chief complaints at presentation were edema as nephrotic syndrome 20(69%), non-nephrotic proteinuria 4(13.8%), dyspnea 2(6.9%), weight loss 2(6.9%) and facial edema 1case (3.4%). Fifteen cases (51.7%) were not accompanied by disease (idiopathic group) and 14cases were associated with diseases (disease associated group) such as hepatitis R virus (HBV) infection 10(34.5%) with healthy carrier 5, chronic hepatitis 3, liver cirrhosis 1 and hepatocellular carcinoma 1; systemic lupus erythematosus 1; hyperthyroidism 1; pulmonary tuberculosis 1; dilated cardiomyopathy 2 (1 with HBU infection); diabetes mellitus 1case (with HRV infection). Laboratory findings showed as follows: all of the cases were in normal levels of BUN and serum creatinine; total urine protein/day was higher in idiopathic group (7347±5018mg/day) than that of disease associated group (5763±4175mg/day); hematuria (more than 5RBCs/H,P,F.) was noted 6(40%) in idiopathic and 5cases (35.7%) in disease associated group. Conclusion: Presumed causes of secondary MGN were suggested HBV infection, systemic lupus erythematosus, hyperthyroidism, hepatocellualar carcinoma, diabetes mellitus, pulmonary tuberculosis and dilated cardiomyopathy. Especially HBV infection is the most significant cause of the disease in Korea.