The aim of this study was to investigate the effectiveness of conceptual change-based instruction and traditionally designed physics instruction on students' understanding of projectile motion concepts. Misconceptions related to projectile motion concepts were determined by related literature on this subject. Accordingly, the Projectile Motion Concepts Test was developed. The data were obtained through 43 students in an experimental group taught with learning activities based on conceptual change instruction and 39 students in a control group who followed traditional classroom instruction. The results showed that conceptual change-based instruction caused significantly better acquisition of conceptual change of projectile motion concepts than the traditional instruction. (Contains 3 tables.)