‘Haiibuki’ is a giant embryo rice cultivar that contains abundant γ-aminobutyric acid (GABA) compared with conventional rice cultivars. Here, we performed a functional evaluation of ‘GABA-enriched brown rice’ (GEBR) prepared by modifying the ‘Haiibuki’ cultivar to contain more GABA. Study 1: Spontaneously hypertensive rats were divided into three groups [control (cornstarch), normal brown rice, and GEBR] and fed an orally administered diet for 4 wk. A significant blood pressure elevation-inhibitory effect was observed in the GEBR group as compared with the other groups. Study 2: Rats were divided into two groups and fed ad libitum for 12 wk. The two groups were control (commercial feed with 5% cornstarch) and GEBR (commercial feed with 5% GEBR). Body weight, blood pressure, food consumption, and water intake were measured during the study period, and blood chemistry was analyzed after the study. Plasma 8-hydroxy-2′-deoxyguanosine (8-OHdG) and urinary isoprostane were measured 12 and 10 wk after the start of the study, respectively. A significant blood pressure elevation-inhibitory effect was observed in the GEBR group. The 8-OHdG and isoprostane levels were significantly lower in the GEBR group than in the control group, demonstrating an oxidative stress-reducing effect. Therefore, GEBR exhibited a blood pressure elevation-inhibitory effect under the conditions of this study. The antioxidative action may occur secondarily to the antihypertensive action of GABA, suggesting that the long-term ad libitum ingestion of GEBR prevents hypertension. A reduction in oxidative stress could reduce the chances of complications in cardiovascular diseases.