Abstract:Background: The EASI Survey, a 20-item parent report, was one of the first instruments developed to measure children's temperament. Methods: We performed an exploratory factor analysis (EFA) of the EASI items in a randomly halved population of Japanese fathers (n = 237) and mothers (n = 412) of children under four years of age. The factor structure was cross-validated by a confirmatory factor analysis (CFA). Then, parents' assessments of each temperament were regressed on the other parents' assessments and then on a variety of intrapersonal and interpersonal variables related to the assessor parents. Results: An EFA yielded a two-factor structure but a four-factor structure according to the original report showed better fit with the data. The new four-factor model (excluding items with low factor loadings) showed in a CFA acceptable goodness-of-fit with the data. This four subscales showed moderate internal consistency. Parental assessment of the EASI subscales was explainable by the assessment rated by the other parent. After controlling it, parents with depression, anger, and less caring attitudes were more likely to rate their child's Emotionality and Impulsivity higher than their partners. Conclusions: The EASI Survey may be applicable to a Japanese non-clinical child population.