Changes in the antioxidant capacity of albumin and alterations of the albumin structural conformation were examined in patients in advanced stages of diabetes nephropathy. Human serum albumin was purified from diabetic patients in pre-dialysis (glomerular filtration rate [GFR] between 15 and 29 ml min(-1) 1.73 m(-2)) and those in dialysis (GFR ≤ 15 ml min(-1) 1.73 m(-2)) and then compared with albumin from patients with a normal GFR (>90 ml min(-1) m(-2)). We evaluated the antioxidant capacity of albumin using an enhanced chemiluminescence-based assay and thiol group content, and the structural changes were evaluated by circular dichroism and fluorescence spectroscopy. The antioxidant capacity and thiol content of albumin from patients in advanced stages of diabetic nephropathy were markedly reduced. The circular dichroism spectra showed a mean albumin α-helix content reduction from 44 to 37 % and from 44 to 30 % between the control group and pre-dialysis and dialysis patients, respectively. Additionally, the fluorescence intensity was reduced by 4.2 and 13 % for the groups 4 and 5, respectively, in relation with the control. These data provide evidence for the partial denaturation of albumin and exacerbated oxidative stress among patients in advanced stages of diabetes nephropathy before and even after dialysis.