This article is interesting in ostensive forms of two physical education (PE) teachers within the activity of Swimming in Tunisia. Its objective is to analyze the ostensive forms of PE teachers and to extricate their effects on the relationship to knowledge. The methodology of the research is qualitative. It subscribes in the field of didactic clinical interactions of PE and on the clinical analysis of teaching practice of an experimented and a novice teacher in order to glimpse « case by case » the singular subject (Terrisse, 1999). Data collection and analysis subscribe in the constructed temporality in one time of professorial action. The test (Terrisse, 2000) relies on the knowledge ostension scale (Robert, 2012; Salin, 2002). Results put in evidence that PE teachers use ostensive forms to influent the relationship to knowledge in Swimming.