This study aimed to investigate the effects of a gamma-aminobutyric acid (GABA) rich tomato (Solanum lycopersicum L.) cultivar 'DG03-9' in comparison with 'Momotaro', a commonly consumed tomato cultivar in Japan, on systolic blood pressure (SBP) in spontaneously hypertensive rats (SHR). In a single administration study, treatment with the GABA-rich cultivar elicited a significant decrease in SBP compared to the control group. In a chronic administration study, SHR were fed diets containing one of the tomato cultivars for 4 weeks. Both cultivars significantly reduced the increase in SBP compared to the control. The antihypertensive effect of the GABA-rich cultivar was higher than that of the commonly consumed cultivar in both the single- and chronic-administration studies. Treatment with a comparable amount of GABA elicited a similar response to treatment with the GABA-rich cultivar. These results suggest that the GABA-rich cultivar 'DG03-9' is a potent antihypertensive food and may be useful for treating hypertension effectively.