We studied power spectral analysis of heart rate variability (HRV) in control spontaneously hypertensive rats (SHR) and tourmaline hydroxyl negative ion-treated SHR groups. The power spectrum of HRV in SHR groups was composed of two frequency components; low frequency (LF, 0.005 approximately 1.0 Hz) and high frequency (HF, 1.0 approximately 2.0 Hz) components. The low frequency power (LFP) of HRV spectrum, which indicates sympathetic nervous activity, in negative air ion-treated SHR group was significantly (p < 0.01) smaller than in control SHR group. And also we obtained that the high frequency power (HFP) showing parasympathetic nervous activity in negative air ion-treated SHR group was significantly (p < 0.01) higher than in control SHR group. It could be concluded that hydroxyl negative air ions generated by tourmaline ionizer system decreased the elevated blood pressure, and control the sympathetic nervous activity and the parasympathetic nervous activity in SHR having the elevated blood pressure.