— This paper focuses on the architectural impact of public libraries’ environment on users’ mental health. This study also investigates appropriate criteria and patterns and identify environmental stimuli in life space and their effects on humans and then evaluate environmental indexes. Present study was conducted through unique and innovative research method and tools to examine architectural effects of public library on user’s mental health in all depended public libraries in Tehran (Capital city) of Public Libraries’ institution of Iran. A 41-item checklist is designed by the researchers, which provides standards, criteria and patterns for indoor and outdoor space of public libraries. This study examines via descriptive-survey method and two types of quaternaries were used as assessment tools: General Health Questionnaire (GHQ) and researcher-made questionnaire based on architectural theories. The results indicate that architectural space of public libraries is effective on users’ mental health. This research study confirms that there is a significant relationship between architectural implications and characteristics of public libraries and users’ mental health