The effect of the intake of apple vinegar containing yuzu juice on psychological stress was investigated in healthy young women. The subjects used in this study were 16 healthy female university students (22 ± 1 years old), who ingested 100mℓ of the apple vinegar drink twice a day (before breakfast and before supper) for 3 weeks. Next, the changes in the mental stress indices of the group that consumed the drink were compared to those of the control group. In the test, the subjects ingested 100mℓ of the test beverage. 30 minutes after the ingestion, they were subjected to a stressor, which was a simple mental task. After this, they were given a 60-min rest. Blood flow and heart rate variability measurements, electroencephalography, and a visual analog scale (VAS) were used to determine the mental stress indices. The blood flow, parasympathetic nerve activity index, and alpha/beta ratio in the group that consumed the drink were significantly higher than those in the control group. There was a correlation between blood flow and alpha waves. From these results, the apple vinegar drink was shown to have a psychological stress-reducing effect.