Rapid urbanization and uncontrolled expansion of urban spaces in recent decades have caused multiple challenges in the physical, social, and particularly environmental dimensions of cities. Behshahr, as a city with significant natural, ecological, and cultural values, faces increasing pressures from inappropriate urban development and population growth, posing a serious threat to environmental sustainability, residents’ quality of life, and the ecological capacity of the region. This study aims to conduct a comprehensive structural analysis of Behshahr’s urban fabric with a specific focus on environmental sustainability. The research adopts a descriptive–analytical methodology, relying on both field observations and documentary data. The statistical population consists of experts and specialists in urban planning, architecture, and environmental management. Data were collected through structured questionnaires and analyzed using SPSS and Smart PLS software to ensure precise and reliable results. Findings indicate that the overall physical structure of Behshahr is below the desired level in terms of environmental sustainability (mean < 3). Among the examined components, “housing and buildings,” “land use,” and “urban morphology” had the most significant impact on sustainability outcomes, whereas “land characteristics” and “zoning” did not show meaningful effects. These results emphasize the need to improve construction management, revise land-use policies, optimize land utilization, and systematically organize the urban fabric to reduce environmental pressures and enhance urban resilience. Ultimately, the study demonstrates that achieving long-term environmental sustainability in Behshahr requires strategic changes in structural and managerial patterns, moving toward a compact, resilient, and ecologically harmonious city where urban development aligns with natural and ecological capacities, ensuring a sustainable, livable, and safe future for current and future generations.