OBJECTIVES To use blood oxygen level dependent (BOLD) magnetic resonance imaging (MRI) to evaluate renal oxygenation in patients with primary nephrotic syndrome (PNS), and test the hypothesis that renal tissue oxygenation correlates with renal function, tubulointerstitial alterations and treatment response. METHODS Patients with untreated first-onset PNS and healthy control subjects underwent BOLD MRI. Blood and urine samples were obtained on the day of MRI, and patients underwent renal biopsy the day after MRI. Renal tubulointerstitial damage scores (TIDS) were determined using Katafuchi criteria. All patients received corticosteroids within 7 days after MRI and were followed up for 12 months. RESULTS Medullary R2* values were significantly lower in patients with PNS (n = 20) than controls (n = 18). Medullary R2* values were negatively correlated with estimated glomerular filtration rates and positively correlated with TIDS in patients with PNS. There were no significant differences in medullary or cortical R2* values when patients were classified according to treatment response. CONCLUSIONS The medullary oxygen concentration was higher in patients with PNS than in control subjects. BOLD MRI was a useful noninvasive method for the evaluation of renal function and tubulointerstitial impairment.