Background: The urban open spaces and their effects on the physical and mental health highlights the attention on the quality of such spaces. Thermal comfort is an environmental component affecting the reactionary behavior of people in these spaces. The present study aimed to investigate the relationship between mental components and landscape structure and its effects on the thermal assessment of individuals. Methods: In this study, we used the descriptive method for explaining the mental components and landscape structure. Then, the survey method was employed for determining the correlations between research variables. Finally, we used the experimental method for testing the variables using specific tools. Thermal analysis was done by computer simulation method using ENVI-met software in the Karoon river area in Ahvaz City, Iran. UTCI (universal thermal climate index) is the index used for assessing thermal comfort. To find out the relationship between the research variables, the field data were randomly collected by questionnaires using the Cochran formula. Results: The findings demonstrated the existence of a relationship between landscape structure and different mental states in individuals. The moods of the individuals in open spaces affect their perceptions of the landscape and thermal assessment of the environment. Conclusions: Eventually, and based on the study findings, it was found that people’s mental states in different situations affect their perception of the landscape’s quality and structure and reactionary behavior. It also influences their thermal assessment.