The aim of this study was to investigate the effects of vegetable tablets containing Gamma-Aminobutyric Acid (GABA) intake on cardiovascular response and the autonomic nervous system in young adults. In a double-blind, randomized controlled trial, 7 healthy subjects were assigned to take vegetable tablets (10 g/trial) or control tablets (10 g/trial). We measured heart rate (HR), systolic and diastolic blood pressure, stroke volume, cardiac output, total peripheral resistance index, and the low- and high-frequency oscillatory components of heart rate variability (HRV). Two major spectral components were examined at low-frequency (LF: 0.04–0.15 Hz) and high-frequency (HF: 0.15–0.4 Hz) bands to indicate HRV. There were significant interactions in HR ( p <0.01) and in LF/HF of HRV ( p <0.05). HR increased after intake of control tablets, but not after that of vegetable tablets. LF/HF increased rapidly after intake of control tablets and rose slightly after vegetable tablet intake. There was no significant difference between the vegetable and control tablet trials in stroke volume, cardiac output, total peripheral resistance, systolic or diastolic blood pressure, HF, or LF. In conclusion, these results suggest the possibility that single administration of vegetable tablets containing GABA suppresses the sympathetic nervous activity leading to an elevation of blood pressure.