The present study was designed to investigate the effects of color temperature of lighting sources on a contingent negative variation (CNV). Eleven male students (mean age, 23.2) volunteered as subjects. The CNV was recorded under three different color temperature conditions (3000°K, 5000°K and 7500°K). The illuminance level was kept at 1000lx. The lighting condition caused no effect on the reaction time of the performance included in the CNV paradigm. On the other hand, the CNV was suggested to be influenced by the lighting condition. Especially, the CNV between 1025 msec to ll25 msec after the warning stimulus (S1) under 7500°K was obviously larger than that under 3000°K. This tendency was observed within the range between 800 msec and 1300 msec. Judging from no correlation between the light condition and reaction time, the concept of readiness potentials has little possibility for explaining the difference in CNV between the lighting conditions. Therefore, the difference in CNV between 3000°K and 7500°K was conclud-ed to be originated from some differences in orienting response. The color temperature of 7500°K was considered to be more activating than the color temperature of 3000°K from the view, point of reticular activating system in CNV mechanism