Objectives: The knowledge, attitudes, beliefs and behaviours of health professionals are important in the successful application of exercise programs for the treatment of people with mental illness. We developed the Exercise in Mental Illness Questionnaire-Health Professionals Version (EMIQ-HP) in response to the lack of a comprehensive, valid and reliable instrument to assess the knowledge, attitudes, beliefs and behaviours of health professionals. Methods: Content validation was achieved by expert consensus. Testeretest reliability was calculated using intraclass correlation coefficients. Results: Thirty health professionals completed the questionnaire on two occasions separated by seven days. With the exception of one item, ICCs ranged from 0.61 to 1.00 suggesting excellent testeretest reliability. Conclusions: We propose the EMIQ-HP may be used to assess the knowledge, attitudes, beliefs and behaviours of health professional regarding the prescription of exercise of people with mental illness. Further trialling and psychometric testing is recommended.