Abstract –In this paper we investigate students’ conceptions of “geometric locus” by using the cK¢ model. For this purpose, we formed 6 g roups, each of which consisted of two 10th grade students, who were studying in a big city in the Central Anatolian region. We asked the participants 5 questions related to the “geometric locus” concept. In light of the literature, we firstly revealed the conceptual structure of “geometric locus”. Later, students’ conceptions about this concept have been analyzed by comparing stud ents’ responses to these questions and conceptual structure of “geometric locus” concept. The analyses we have conducted with the data suggest that students’ conceptions were not convenient, moreover; they did not have exact conceptions about the core of concepts and they were not able to correctly explain each situation. Although the main focus was on the “geometric locus”, we have obtained interesting outcomes related to “graphic”.