(-)-Epigallocatechin-3-gallate (EGCG), which is largely found in green tea, is known to eliminate reactive oxygen species and associated inflammatory responses in vitro and in cells. However, the in vivo mechanisms underlying the effects of EGCG on the amelioration of metabolic disorders are not fully understood. In this study, we examined whether dietary supplementation with EGCG reduces inflammatory responses in peripheral leukocytes of a non-obese type 2 diabetes animal model, Goto-Kakizaki (GK) rats. GK rats at 9 wk of age were fed a control high-fat diet (46 energy % from lard and corn oil) or a high-fat diet containing 0.1%, 0.2%, or 0.5% EGCG (w/w) for 25 wk. The oxidative stress markers 8-hydroxydeoxyguanosine (OHdG) and total malondialdehyde (MDA) were reduced by supplementation with EGCG at 0.1%, but not at 0.2% or more. Significant reductions in the mRNA levels of genes related to inflammatory responses (TNF-α, IFN-γ, IL-1β, IL-6, IL-18, MCP-1, CD11b, and S100a6), 8-OHdG, and total MDA were induced in peripheral leukocytes of GK rats by EGCG supplementation at 0.1%, but not at 0.2% or more, compared with rats fed the control diet. The present results suggest that supplementation with a low dose of EGCG reduces oxidative stress and the expressions of genes involved in inflammation in peripheral leukocytes of GK rats.