The purpose of our study to contrast the P300 and vigilance indicator in hot and humid condition. Sixteen participants performed this experiment. The participants are university students with nationality Japanese (eight participants) and Indonesia (eight participants). Indonesia participants conducted four experimental conditions: standing position and natural condition (without Air Conditioning and fan), standing position and used a fan, standing position and used Air Conditioning, and sitting position and used Air Conditioning. Japanese participants conducted only one experimental condition (standing position and natural condition (without Air Conditioning and fan). P300 and vigilance indicators were measured before and after the given task. Event-Related Potential (ERP) P300 and Psychomotor Vigilance Task (PVT) were accommodated for P300 and vigilance indicators. According to the measurements, the task performances of the Indonesia participants among interaction between the subjects and the contrasting conditions were significantly different in ERP P300 latency (p<0.05), ERP P300 potential (p<0.05), and mean reaction time of PVT (p<0.05). On standing position and natural conditioning, P300 and PVT were not significantly different by nationality (Indonesia and Japanese students). Results showed that high temperature and humidity in the Japan summer season decreased P300 and vigilance, particularly for natural conditions.