The aim of this study was to develop a valid and reliable instrument to measure Turkish kindergarten students' understandings of some science concepts and scientific inquiry processes which are grounded in the Turkish Preschool Curriculum. The sample of the study was 371 kindergarten students, 12 Subject Area Experts (SAE), and 7 Turkish Language Experts (TLE). Six stages were followed in the development process of the instrument: (i) item formulation, (ii) content validity, (iii) language validity, (iv) item difficulty and discrimination index, (v) factor analysis, and (vi) reliability. First, an item pool was constituted with 42 items. Second, SAEs and TLEs rated these items in respect to the degree to which they reflected the content and their understandability and grammar accuracy in Turkish. Third, all items were implemented kindergarten students, and 26 items were eliminated according to their item difficulty and discrimination index values. Last, factor analysis and reliability were studied by means of the data belonging to the rest of items. Results revealed that the instrument with 16 items had two factor structure and acceptable reliability.