Background : Ginger ( Zingiber officinale ) is one of the functional foods which contains biological compounds including gingerol, shogaol, paradol and zingerone. Ginger has been proposed to have anti-cancer, anti-thrombotic, anti-inflammatory, anti-arthritic, hypolipidemic and analgesic properties. Here, we report the effect of ginger supplementation on glycemic indices in Iranian patients with type 2 diabetes. Methods : A double-blind, placebo-controlled, randomized clinical trial was conducted on 20–60 -year-old patients with type 2 diabetes who did not receive insulin. Participants in the intervention and control groups were received 3 g of powdered ginger or placebo (lactose) (in capsules) daily for 3 months. Glycemic indices, total antioxidant capacity (TAC), malondialdehyde (MDA), C-reactive protein (CRP), serum paraoxonase, dietary intake and physical activity were measured at the beginning and end of the study, and after 12 h fasting. Results : Comparison of the indices after 3 months showed that the differences between the ginger and placebo groups were statistically significant as follows: serum glucose (–19.41±18.83 vs. 1.63±4.28 mg/dL, p<0.001), HbA 1c percentage (–0.77±0.88 vs. 0.02±0.16 %, p<0.001), insulin (–1.46±1.7 vs. 0.09±0.34 μIU/mL, p<0.001), insulin resistance (–16.38±19.2 vs. 0.68±2.7, p<0.001), high-sensitive CRP (–2.78±4.07 vs. 0.2±0.77 mg/L, p<0.001), paraoxonase-1 (PON-1) (22.04±24.53 vs. 1.71±2.72 U/L, p<0.006), TAC (0.78±0.71 vs. –0.04±0.29 µIU/mL, p<0.01) and MDA (–0.85±1.08 vs. 0.06±0.08 µmol/L, p<0.001) were significantly different. Conclusions : This report shows that the 3 months supplementation of ginger improved glycemic indices, TAC and PON-1 activity in patients with type 2 diabetes.