This study investigated the effects of Acorus gramineus aroma on electrical activity in the brain as evaluated by an electroencephalogram (EEG). The subject was 20 healthy female young adult. EEG electrodes were attached at the frontal, temporal, occipital, and parietal lobes according to the international 10-20 system. The subject was exposed to Acorus gramineus aroma for a period of 1 minutes each before, and after aroma smelling. Acorus gramineus aroma increased the alpha power/beta power ratio on the frontal and parietal lobes of the brain. These increases induced by the increased alpha power. The increased alpha power induced calmness and stable status. It is concluded that Acorus gramineus aroma diminishes the state of wakefulness in the brain; alpha powers/beta powers ratio was decreased in the brain of subject. Acorus gramineus aroma may be used for a sleep-inducing effect.