We report the case of a 67-year-old man with allergic granulomatosis and angiitis (AGA; Churg-Strauss syndrome) who developed nephrotic syndrome during his clinical course and demonstrated membranous nephropathy on renal necropsy by electron microscopy. Following the development of symptoms of bronchial asthma accompanied by eosinophilia and mononeuritis multiplex, transbronchial lung biopsy confirmed a diagnosis of AGA. The patient died of pneumonia and disseminated intravascular coagulopathy, but necropsy revealed severe tubulo-interstitial damage with neutrophilic infiltration and, in half of the glomeruli, mesangial proliferation with subepithelial dense deposits. This paper thus describes a rare case of AGA complicated by a secondary type of stage I membranous nephropathy.