We report a case in which diffusion-weighted magnetic resonance imaging (DWI) demonstrated renal artery stenosis-related renal ischemia and the therapeutic efficacy of revascularization. The patient was a 73-year-old man, who underwent descending thoracic aortic replacement due to DeBakey IIIb chronic aortic dissection, and who showed progressive renal dysfunction due to right renal artery stenosis caused by false lumen thrombosis. DWI demonstrated a decreased apparent diffusion coefficient (ADC) in the right kidney, indicating renal ischemia. Angioplasty with stenting restored renal perfusion and improved the renal function, resulting in the normalization of the decreased ADC in the treated kidney. Thus, DWI can be used to monitor renal ischemia in cases involving advanced renal artery stenosis.