The aim in this study was to understand the effects of project-based curricula on 6-year-old preschool children's conceptual development. Two classes of 14 preschoolers were assigned at random, 1 to the experimental group and the other to the control group. The experimental children's group took part in project-based educat ion for a total of 12 weeks while the control group followed the regular preschool curriculum. Data about the children's conceptual development were gathered using the Bracken Basic Concept Scale-Revised (Bracken, 1998), which was previously adapted for 6-year-old Turkish children by Biittin Ayhan and Aral (2007). The results revealed that all children improved their scores between the time of pretest and posttest, but there was a small difference in favor of the experimental group in the posttest scores.