The purpose of this study was to identify the effects of essential oil inhalation on the 24-hour ambulatory blood pressure (BP) and salivary cortisol level in 83 prehypertensive and hypertensive subjects. The experimental group (n = 28) was asked to inhale an essential oil blended with lavender, ylang-ylang, marjoram, and neroli (20 : 15 : 10 : 2), whereas the placebo group (n = 27) was asked to inhale an artificial fragrance for 24 hours and the control group received no treatment (n = 28). The SBP (P < .001) and DBP (P = .009) measured at home in the experimental group were significantly decreased compared with the placebo group and the control group after treatment. The daytime SBP during the 24-hour ambulatory BP measurement of the experimental group presented with significant decreases in comparison with the measurements of the placebo group and the control group (P < .001). There was no statistically significant difference in the nighttime SBPs. The daytime DBPs during the 24-hour ambulatory BP measurements of the experimental group presented with significant decreases in comparison with the measurements of the placebo group and the control group (P = .002). There was no significant difference in the night time DBPs. The experimental group showed significant decreases in the concentration of salivary cortisol in comparison with the concentrations of the placebo group and the control group (P = .012). In conclusion, the inhalation of an essential oil had immediate and continuous effects on the home SBP, daytime BP, and the stress reduction. Essential oils may have relaxation effects for controlling hypertension.