Background: Adequate knowledge of the metabolic syndrome is essential for mental health nurses as it enhances their ability to recognize and address the physical needs of individuals diagnosed with serious mental illnesses.Aims: This study investigated the factors influencing the level of metabolic syndrome knowledge among mental health nurses.Methods: A cross‐sectional study was conducted with 208 mental health nurses recruited from four hospitals in northern Taiwan, including two regional hospitals, one medical center, and one mental health hospital. Nurses’ knowledge was assessed using a validated 20‐item self‐administered questionnaire covering key aspects of metabolic syndrome, including pathophysiology, diagnostic criteria, and management. The questionnaire demonstrated satisfactory reliability (KR‐20 = 0.702) and content validity. Data analysis involved descriptive statistics, independent t‐tests, one‐way analysis of variance, Pearson correlation coefficient, and generalized linear models to identify predictors of knowledge levels.Results: The overall correct answer rate was 60.1%. Generalized linear modeling demonstrated that nurses’ knowledge was significantly associated with their sources of information (B = 1.371, 95% CI = 0.458–2.285, p = 0.003), the type of hospital they worked in (B = −1.027, 95% CI = −2.015 to −0.039, p = 0.042), and working in a community unit (B = 1.975, 95% CI = 0.067–3.883, p = 0.042).Conclusions: Our results indicate that mental health nurses possessed a moderate level of knowledge concerning metabolic syndrome in people diagnosed with serious mental illness. Addressing this gap requires targeted education programs that integrate physical health education into psychiatric care and promote the use of diverse, evidence‐based resources tailored to the specific needs of mental health nurses in different settings. Organizational efforts should focus on fostering a supportive culture that enhances access to high‐quality resources, encourages interdisciplinary collaboration, and supports continuous professional development.