Background: Physiotherapists (PTs) are responsible for the prevention and promotion of physical and mental health. Their beliefs toward mental illness (MI) are important to disclose stigmatization. Purpose: To investigate the beliefs of PTs toward MI. Methods: Beliefs toward Mental Illness Scale were sent to an e-mail network of Turkish Physiotherapy Association. The scale has three subscales: 1) Dangerousness; 2) Incurability and Poor Social and Interpersonal Skills (IPSIS); and 3) Shame. Total and subscale scores were used for analysis as higher scores indicated more negative beliefs. Results: In total, 155 PTs completed the questionnaires. The median total score was 45/105, while Dangerousness, IPSIS, and Shame scores were 20/40, 23/55, and 0/10, respectively. Dangerousness score was higher in PTs with a bachelor's degree compared to PTs with a postgraduate education (p = .049). IPSIS score was higher in PTs who did not consult a health professional in the presence of MI compared to PTs who consulted (p = .023). Total and IPSIS scores were higher in PTs exposed to an individual with MI during physiotherapy sessions compared to PTs having a family member with MI (p = .006 and p = .012, respectively). Conclusion: Postgraduate education may affect the positivity of the beliefs regarding the dangerousness of MI. Negative beliefs about the curability of MI, frustration in interpersonal relationships, and perception that the mentally ill are untrustworthy may hinder the health-seeking behavior, even the individual is a health-care professional. Having a family member with MI may positively affect the beliefs of PTs in case of an exposure to a patient with MI during physiotherapy sessions.