BACKGROUND: Facilitating the healing process of patients with psychiatric disorders depends on high‑, quality mental health care and expert psychiatric nurses. A valid tool is required to objectively evaluate the quality of performance and competency of psychiatric nurses. This systematic review aimed to investigate and critique the psychometric properties of some psychiatric nursing clinical competency assessment instruments with Consensus‑, based standards for the selection of health status measurement instruments (COSMIN) checklist and according to Preferred Reporting Items for Systematic Reviews and Meta‑, analyses (PRISMA). MATERIALS AND METHODS: To retrieve published articles using Persian and English keywords “, psychiatric nursing, ”,“, competence, ”,“, competency, ”,“, tool, ”,“, checklist, ”,“, scale, ”,“, questionnaire, ”,“, psychiatric mental health nurse, ”,were searched in databases without time limitation. Then, psychometric properties of selected instruments were evaluated using the COSMIN checklist and reported according to the PRISMA statement. RESULTS: Most of these tools did not entirely and desirably report psychometric properties. It is not designed as a special tool for postgraduate psychiatric nursing. CONCLUSION: The methodology of existing instruments does not meet the COSMIN checklist criteria,therefore it needs to develop. To assess the competency of psychiatric nursing postgraduate, a tool tailored to the cultural and social context and with acceptable psychometric properties is necessary.