The protective effects of Phaleria macrocarpa (PM) against oxidative stress in diabetic rats were investigated. Diabetes was induced in male Sprague Dawley rats using alloxan (150 mg/kg i.p). After the administration of PM fractions for two weeks the diabetic symptoms, nephropathy and renal antioxidant enzymes were evaluated. The results showed that the oral PM treatments reduced blood glucose levels in diabetic rats. The PM fractions decreased kidney hypertrophy and diminished blood urea nitrogen (BUN) in diabetic rats. Malondialdehyde (MDA), a lipid peroxidation marker, was increased in diabetic animals, but was suppressed by the PM treatments. In addition, the superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities, and glutathione (GSH) level in the alloxan-induced diabetic rats were significantly decreased compared with those in the normal rats, but were restored by PM treatments. The PM fractions also suppressed the level of MDA in the kidney. In conclusion, the anti hyperglycemic and anti-nephropathy of P. macrocarpa may be correlated to the increased renal antioxidant enzyme activity in the kidney.