In this paper, the power spectral analysis of heart rate variability(HRV) was performed to evaluate effects of orthostatic stress with head-up tiIt on autonomic nervous system(ANS) for 25 healthy male subjects(age : 24 $pm$ 5 yr.) and a new method was proposed to assess the autonomic balance. The ECG and respiration signals were recorded at tiIt angles of $0^{circ}$, $45^{circ}$, $90^{circ}$and $0^{circ}$ successively for 10 minutes per each stage under the condition of frequency controlled respiration(0.25Hz). Heat rate(HR) gradually increased ils the angle increased Similarly, according to the increment of angle, normalized low frequency component(0.05-0.15Hz) gradually increased, whereas normalized high frequency component (0.20-0.30Hz) was reduce4 From these results it is speculated that orthostatic stress head-up tiLt, results in the prevalence of sympathetic tone in autonomic balance with the increment of sympathetic tone and the decrement of parasympathetic tone, which seems to meanthat autonomic nervous system plays a major role in compensating for disturbances of cardiovascular system due to it.