The concept of positive occupations that enhance physical, mental, and social well-being is a novel idea that integrates positive psychology and occupational therapy. Valid and reliable scales are required to assess positive occupations for well-being in mental health settings. In this regard, the Assessment of Positive Occupation-15 (APO-15) is unique, as it evaluates positive occupations that promote health and well-being. This study aimed to investigate the validity and reliability of and determine the cutoff value of the Turkish version of the APO-15 in individuals with serious mental illness (SMI). The study was conducted with 106 individuals with SMI. The structural validity of the scale items was determined using confirmatory factor analysis, while the reliability of the scale was analyzed with Cronbach's alpha (α) and McDonald's omega (ω) coefficients. The comparative fit index (0.964) and the Tucker-Lewis index (0.955) demonstrated a good fit. Cronbach's alpha coefficients were .826, .814, .707, and .674, and the total scale score was 0.924. McDonald's ω coefficients for the four scale dimensions were 0.832, 0.818, 0.716, and 0.727. The cutoff point of 49.50 for the APO-15 for point sensitivity (0.727) and specificity (0.766) yielded good results. The Turkish version of the APO-15 is an effective and reliable tool for assessing well-being in mental health settings.