The present study was designed to investigate the effects of color temperature of lighting sources on the heart rate variabiiity. Eight male students volunteered as subjects. The heart rate variability during task and rest sessions were estimated under nine different lighting environments consisting of three levels of color temperature (3000°K, 5000°K and 6700°K) and three levels of illuminance (1001x, 3001x and 9001x). The lighting condition caused no effect on the mean heart rate. On the other hand, the power spectrum of heart rate was significantly influenced by the lighting conditions. The respiratory sinus arrhythmia component and Mayer wave related sinus arrhythmia component of the power spectrum increased under higher color temperature conditions. Judging from the consistency of heart rate level, the balance between the effects of parasym-pathetic and sympathetic nervous systems remained at a constant level irrespective of lighting quality and intensity. Therefore, both parasympathetlc and sympathetic nervous functions were concluded to be enhanced under higher color temperature conditions. The light with higher color temperature was considered to activate the autonomic nervous function more than the light of lower color temperature. The effect of color temperature was much remarkable in the rest session comparing with the task session. This fact was discussed from the viewpoint of color temperature effect in environmental lighting.