A 57-year-old Japanese woman with a 5-year history of rheumatoid arthritis (RA) was admitted to our hospital for an evaluation of nephrotic range proteinuria (4.8 g/day). A renal biopsy led to the diagnosis of amyloidosis according to strong positivity for Congo red staining and the detection of microfibrillar structures on electron microscopy that were negative for AA and positive for kappa light chain. Combination therapy with high-dose melphalan and autologous stem cell transplantation was performed according to the regimen for AL amyloidosis. Her proteinuria and RA subsided, but relapsed after 3 years. This is the first report regarding kappa light chain amyloidosis in an RA patient.