Objective: To assess the kidney oxygen bioavailability in acute renal failure using blood oxygen level dependent (BOLD) magnetic resonance (MR) imaging. Methods: Twenty-one patients with acute renal failure,including 18 patients with oliguric renal failure,1 nonoliguric acute renal failure and 2 functional renal failure were enrolled in the study; 20 healthy subjects served as controls.All subjects received renal functional MR examination.BOLD MR imaging with 16 gradient-recalled-echoes on a 1.5-T scanner were performed.R2~*(1/sec) values of the cortex and medulla and R2~* ratio of the medulla to cortex (R2~* ratio of M/C) of the renal were recorded respectively. Results: The R2~* values of the medulla was higher than those of the cortex in controls (17.64±1.86/sec vs 13.73±0.49/sec,P<0.00).The R2~* ratio of M/C in controls was 1.28±0.06.The R2~* values of the medulla (13.31±4.28/sec) and cortex (12.25±2.41/sec) and the R2~* ratio of M/C (1.01±0.25) in oliguric renal failure were lower than those in controls (P <0.05).Patients with functional renal failure and nonoliguric acute renal failure had higher R2~* values in cortex and medulla and higher R2~* ratio of M/C than those of controls. Conclusion: BOLD MRI demonstrates that decreased R2~* values of cortex and medulla suggest lower oxygen bioavailability in acute renal failure and decreased R2~* ratio of M/C suggests the disappearance of a steep cortico-medullary gradient of oxygen.