The purpose of this study was to develop a School Readiness Inventory for kindergarteners. The School Readiness Inventory for kindergarteners was developed by a series of data collections and analyses. The School Readiness Inventory was originally composed of 135 items based on previous studies and a preliminary survey of teachers and mothers. Eighty items out of 135 were selected for the School Readiness Inventory by a number of experts. In the pilot study, 60 items out of 80 were selected based on their psychometric properties. In the main study, a 60-item-version of the School Readiness Inventory was used to collect data from the teachers of kindergarteners. Finally, the number of items was reduced to 36 using factor analyses. The preliminary School Readiness Inventory consisted of 4 basic categories: physical health and motor development, cognitive development and general knowledge, social-emotional development, and daily life habits and attitudes. Validity, both in terms of content and social factors were confirmed by a number of experts. The construct validity of the School Readiness Inventory was supported by means of factor analyses. There were four factors in the School Readiness Inventory: readiness for group activities, emotional competence, basic knowledge of daily life, and readiness for learning. The reliability of the School Readiness Inventory was confirmed using Cronbach Alpha, test-retest reliability, and split-half reliability testing.