The tree peony is an important ornamental plant with many cultivars and rich fragrances. The scents released from the flowers of various tree peony cultivars might impose different influences on psycho-physiological responses, which seem to be the gap in the present research. Methods: We investigated psycho-physiological responses of 80 students (23.9±2.25 years old) to the olfactory stimulation by the four types of tree peony fragrances, including the phenolic scent (PS), rose scent (RS),

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... scent (WS), and lily of the valley scent (LVS). The present study assessed autonomic parameters such as heart rate (HR) and heart rate variability (HRV) to determine the arousal levels of the autonomic nervous system. Psychological evaluation was carried out using the Profile of Mood States (POMS) and semantic differential methods (SDM). Electroencephalography (EEG) was recorded during tree peony fragrance inhalation periods compared with control conditions. Results: The students exhibited significantly higher parasympathetic nervous activities, but significantly lower sympathetic nervous activities and heart rates after inhaling tree peony fragrances. The four kinds of tree peony fragrances induced significantly less negative and more vigorous moods, and obtained better scores in subjective evaluation, especially the rose scent. Furthermore, the analysis of EEGs showed a remarkable increase in the power of low alpha (8-10 Hz), high alpha (10-12 Hz), and theta (4-7 Hz) waves. Conclusions: Our studies demonstrated that a short olfactory stimulation with the four peony scents would be not only a promising therapeutic method for improving physiological function but also an effective psychological relaxation strategy for the