Purpose: To explore knowledge, attitudes, and behaviour related to physical activity (PA) and sedentariness among registered dietitians (RDs) in family health teams in Ontario.Methods: This cross-sectional, descriptive study utilized a semi-structured interview guide to conduct qualitative interviews with 20 RDs. Self-administered questionnaires were used to assess personal PA (short version of the International Physical Activity Questionnaire) and sedentary behaviour (Sedentary Behavior Questionnaire).Results: Thematic analysis indicated that, in general, participants had good knowledge of PA and sedentariness. They were knowledgeable about the PA guidelines. They had positive attitudes toward PA and nonsedentariness, stating that both are important in the prevention and treatment of chronic conditions. Quantitative analysis indicated they had moderate-to-high PA levels and were fairly sedentary.Conclusions: This study supports the position that RDs can serve as excellent role models for PA. Though participants had basic knowledge, RDs may benefit from additional education regarding PA and sedentariness when counselling.