Background Syrian refugees have a high burden of mental health symptoms and face challenges in accessing mental health and psychosocial support (MHPSS). This study assesses health system responsiveness (HSR) to the MHPSS needs of Syrian refugees, comparing countries in Europe and the Middle East to inform recommendations for strengthening MHPSS systems Methods A mixed-methods rapid appraisal methodology guided by an adapted WHO Health System Framework was used to assess HSR in eight countries (Egypt, Germany, Jordan, Lebanon, Netherlands, Sweden, Switzerland, and Türkiye). Quantitative and qualitative analysis of primary and secondary data was used. Data collection and analysis were performed iteratively by multiple researchers. Country reports were used for comparative analysis and synthesis. Results We found numerous constraints in HSR: i) Too few appropriate mental health providers and services; ii) Travel-related barriers impeding access to services, widening rural-urban inequalities in the distribution of mental health workers; iii) Cultural, language, and knowledge-related barriers to timely care likely caused by insufficient numbers of culturally sensitive providers, costs of professional interpreters, somatic presentations of distress by Syrian refugees, limited mental health awareness, and stigma associated to mental illness; iv) High out-of-pocket costs for psychological treatment and transportation to services reducing affordability, particularly in middle-income countries; v) Long waiting times for specialist mental health services; vi) Information gaps on the mental health needs of refugees and responsiveness of MHPSS systems in all countries. Six recommendations are provided to address these issues. Conclusions All eight host countries struggle to provide responsive MHPSS to Syrian refugees. Strengthening the mental health workforce (in terms of quantity, quality, diversity, and distribution) is urgently needed to enable Syrian refugees to receive culturally appropriate and timely care and improve mental health outcomes. Increased financial investment in mental health and improved health information systems are crucial.