A 63-year-old man with an 8-year history of proteinuria was diagnosed with nephrotic syndrome, and a renal biopsy was performed. Light and electron microscopic analyses showed classic features of idiopathic membranous nephropathy (IMN). However, immunofluorescence tests revealed solitary polyclonal granular IgA deposition along the glomerular capillary walls, rather than IgG, which is often dominant in IMN. The combined use of corticosteroids and calcineurin inhibitor was noticeably effective in reducing proteinuria and improving edema in the current case. Two additional rare cases of IMN with solitary IgA deposition were reviewed, and long-term surveillance is still warranted to characterize its clinicopathological features and outcome.