Encouraging patients to be involved in their care and enhancing shared decision making (SDM) have been advocated over the past two decades as means to enhance patient-centered care. However, one of the barriers to implementing SDM in medical consultations is the need to adapt this approach to various populations and medical settings, including mental health, and developing reliable and practical methods for measuring and assessing SDM. This article presents the psychometric properties and validity of an adapted scale, SDM-Q-9-Psy, that assesses SDM in routine care among psychiatric inpatients. Psychiatric inpatients were assigned into an SDM intervention cohort (n = 46) or a control cohort (n = 40). The adapted scale was administered after a decision-making process. The scale was subsequently psychometrically tested via factor and reliability analyses. It was also tested for convergent validity and for its ability to distinguish the degree of SDM between the intervention and control groups (construct validity). The SDM-Q-9-Psy scale yielded a Cronbach's α of .94. Convergent and construct validity parameters were good. The SDM-Q-9-Psy scale can be used to evaluate SDM from psychiatric inpatients' perspective and to provide rapid feedback to mental health professionals, enabling them to monitor their decision-making practice in real-time clinical consultations.