The purpose of the current study was to develop a valid and reliable scale to assess the sibling rivalry behavior of 3-6-year-old preschool children with one or more younger siblings, based on their parents' reports. The pilot study was conducted with 544 parents. Through exploratory factor analysis, six factors were obtained: warmth/closeness, parental partiality, competition, regression and restlessness, antagonism, and negative behavioral changes. The validation study was conducted with 203 parents, using the final version of the scale consisting of 39 items. Confirmatory factor analysis results verified the six-factor solution. The Cronbach's alpha values for the six factors ranged from .63 to .82. The findings showed the reliability and validity of the Preschool Children Sibling Rivalry Scale.