Objective: To observe the relations of 5-HT level in whole blood and physiological state and the behavioral character in the children with autism and provide the clue for the cause and the treatment of autism.Methods:In 35 children in two special education kindergartens and 56 children in a normal kindergarten child autism was screened and diagnosed by using,the Clancy Autism Behavior Scale(CABS),Childhood Autism Rating Scale(CARS),Autism Behavior Checklist(ABC)and ICD-10.The whole blood 5-HT was measured by high pressure liquid chromatography(HPLC)-electrochemistry examines.Results:The level of whole blood 5-HT in 15 children with autism and 56 normal children were(228.68±103.44)ng/ml and(137.46±83.63)ng/ml respectively,the differences had statistics significance.The proportion of 5-HT high concentration(200 ng/ml) in patients was 61.1 % and in normal children was 28.6 %.Using multiple regression analysis,it is the positive correlation in whole blood 5-HT level and serum ferrum iron,and the negative correlation in whole blood 5-HT level and serum zinc and age in the children with autism.It was associated with high 5-HT level in whole blood and the behaviors,etc.Conclusion: 5-HT level may be a biological indicator of autism.