The main purpose of this study was to investigate the psychometric properties of the Ratings of Everyday Executive Functioning (REEF), which was developed for 3-5 years old and validated by Nilsen and colleagues(2017) to evaluate the executive function of preschoolers, and the validity (construct validity, convergent validity, concurrent validity, cross validity) of REEF were examined using three samples of Korean mothers and their children aged 3-5 years. The results of the validity of REEF confirmed through the three samples are summarized as follows: First, after going through the translation-reverse translation and review process by a Korean writer, a preliminary survey was conducted to confirm the clarity and appropriateness of the REEF questions. As a result of the item analysis of REEF, the quality of the items was confirmed, and then the final questions were confirmed. Second, as a result of conducting exploratory factor analysis to examine construct validity, all items except for one item showed an acceptable fit of factor loading, indicating that a single factor was suitable, as in the study that developed the original scale. Third, the correlations between REEF and BRIEF-P, REEF and executive function measured by the execution function performance task were significant, and convergent validity was demonstrated. Fourth, the correlation between mothers’ parenting behavior, preschoolers’ theory of mind, problem behavior and language ability was significant, and concurrent validity was examined. Finally, as a result of cross-validity testing whether the results examined through Study Subject 1 appear the same as the new subject, factor loadings of all items except for the two items were found to be similar. In conclusion, the current study is meaningful in that it provides a new and additional tool for the executive function and REEF validated from various aspects can be used in various ways in the future.