To improve the cognitive performance of preschool, children's electroencephalogram(EEG), concentration level and heart rate variability(HRV) are measured while changing the temperature to 18[°C], 21[°C], 24[°C], 27[°C] and 31[°C] in the test room set as relative humidity 50[RH%], air speed 0.02[m/sec] and illumination 1000[lux]. Measurement condition is uniformly set as 1met of activity while seated and relaxing with the cloth amount of 1.05[clo]. As a result, it was found that sα increased by 40% when the subject was in 24[°C] compared to 31[°C]. Concentration increased by 10[%] under 24[°C] compared to 31[°C]. The standard deviation of normal to normal intervals(SDNN) decreased 12[%] under 24[°C] compared to 31[°C]. Also, aggression decreased by 12[%] under 24[°C] compared to 31[°C]. Therefore, it can be concluded that comfortability and cognitive ability improves under mild temperature such as 21∼24 [°C] better than warm temperature of over 27[°C].