The main purpose of this research is to determine to what extent preservice teachers use visual elements and mathematical properties when they are dealing with a geometrical construction activity. The axiomatic structure of the Euclidian geometry forms a coherent field of objects and relations of a theoretical nature; and thus it constitutes a favorable ground for the learning of the reasoning and justification. In geometry, even if the reasoning is assisted by concrete elements such as drawings, it is not based on actions or spatio-visual elements. Arguments based on mathematical properties are required in geometrical reasoning. A successful teaching of the geometry directly depends on the subject knowledge of the teachers. Another purpose is to map out the different kinds of justifications implemented by teachers related to such an activity. Analyses of the responses indicate that a large proportion of preservice teachers use visual elements for their geometrical constructions and they are tended to use naive empiricism concerning their justifications. (Contains 7 figures and 4 tables.)