[Objective] To examine whether there is a relationship between a child's temperament and his/her behavior and emotional stress expressed during blood collection or vaccination, and consider futuredirections in nursing assistance.[Research method] Scope of survey: The study focused on 76 children between the age of 3 and 7 and their mothers, from whom consent had been obtained, who attended either the pediatric outpatient department of A University Hospital or the outpatient clinic at O Children's hospital for blood collection or vaccination.Survey method: The authors created a questionnaire for completion by the children's mothers, containing 20 questions regarding their "Child's temperament", to which answers ranged from "1. Completely disagree" through to "4. Completely agree".Survey procedure: Use of written questionnaire. At the same time, the children were subjected to saliva sampling prior to and subsequent to injection, and to cooperative behavioral assessment while experiencing pain. Of the 76 mother/child pairs involved in the study, 71 pairs were subjected to analysis (43 boys and 28 girls, average age 61±16 months) once those with incomplete questionnaires and/or saliva samples were eliminated.Statistical analysis: Average cortisol values for the two groups who responded positively and negatively in behavioral assessment were examined using Student t testing, while correlation was examined with Pearson's coefficient of correlation, and factor analysis clarifying the principle of children's temperaments (principal factor method and varimax rotation) was performed using SPSS10.0J for windows to calculate a reliability coefficient.[Results and Discussion] In behavioral assessment, placing a total of 30 children in the "negative reaction" group and 41 children in the "positive reaction" group. Categories out of the 20 in the questionnaire regarding the children's temperament that showed bias in distribution were eliminated, resulting in the extraction of three factors-"anxiety emotion (α = 0.68)", "positivity (α = 0.81)" and "behavioral control (α= 0.68)"- with proper values of 1.000 or higher. A study of the correlations between the children's age in months and the three factors in their temperamental makeup, and their behavioral assessment and saliva cortisol value at the time of injection, showed a positive correlation between behavioral assessment at injection time and the child's age ( r= 0.34, p<0.01), and a negative correlation between behavioral assessment and the "anxiety emotion" factor ( r=-0.35, p<0.01). No correlations were noted regarding other factors. The younger the child, the more likely he/she was to have a negative reaction such as crying. Furthermore, the authors understood that a mother's understanding of anxiety emotion in her child was effective in predicting the child's behavior when he/she was injected. This indicates the need to confirm the child's sense of anxiety with the mother, prior to performing the injection.