The aim of this study was to determine the effects of aromatherapy on oral immune functions and mental states using various essential oils. Saliva samples were collected from 16 adult men before, immediately after, and 30 minutes after aromatherapy using essential oils to measure secretory immunoglobulin A (SIgA) and cortisol levels. Mental states were assessed using the Profile of Mood States 2nd edition (POMS2)—Brief Form. The study was comprised of 7 experiments: 3 experiments used weakly diffused essential oils, 1)Citrus bergamia(BW), 2)Lavandula officinalis(LW), and 3)Citrus limon(CLW); other 3 experiments used strongly diffused essential oils, 4)C. bergamia(BS), 5)L. officinalis(LS), and 6)C. limon(CLS); and 1 experiment did not use any essential oils, 7) only driving an aroma diffuser (CON). Aromatherapy scents were randomly assigned and sessions were carried out for 30 minutes. The secretion rate of SIgA significantly increased 30 minutes after BW aromatherapy, and cortisol concentrations significantly decreased in the BW, BS, and CLW experiments. Mental states were significantly improved by all the essential oils. Notably, C. limon, improved total mood disturbance. Therefore, we concluded that C. bergamia has beneficial effects on oral immune functions and mental stress. In addition, it was confirmed that aromatherapy with essential oils, especially C. limon, is effective in improving mental states.