This study had two purposes; 1) to investigate the fluctuation of autistic children's autonomic arousal level (AAL) among different days and 2) to examine the relationship between AAL and behavior in autism. Five autistic children's heart rates (HRs) at rest were measured once during a break. Their behavior was recorded through the hour. The number of measurement days varied with subject from 8 to 12. The results were as follows. l) Artistic children's HR showed large fluctuation. In case 3,the difference between the highest HR and the lowest HR was 23bpm. 2) The significant relationship between HR and behavior was observed in two subjects. In case 4,stereotyped behavior and hypoactivity related with high HR. When case 5 showed high HR, he wept frequently and didn't come to a teacher when he was called, It was suggested that the occurrence of emotional behavior and social behavior were associated with HR level in case 5.