In recent decades, environmental crises have become one of the fundamental challenges for developing countries, and the need to adopt coordinated and regional policies to address these crises has become increasingly evident. Iran and the Arab League member states possess significant capacity for environmental cooperation due to their geographical, climatic, and economic similarities. However, differences in their environmental policies and practices necessitate a careful comparative study. Therefore, the purpose of this study is to conduct a comparative analysis of the environmental policies of Iran and eight selected Arab League countries (Egypt, Algeria, Iraq, Yemen, Morocco, Saudi Arabia, the United Arab Emirates, and Kuwait), with an emphasis on responsible regionalism and its impact on sustainable development. For this purpose, official UN data for two points in time, 2020 and 2024, were used as the basis for the analysis, and 31 key indicators were extracted within three dimensions: environmental, social, and economic. The research method is mixed, combining quantitative analysis (using Shannon entropy to weight indicators and the TOPSIS model to rank countries) with qualitative library research. The findings are presented in three stages: first, an assessment of environmental policies in 2020; second, a review of developments up to 2024; and third, an analysis of indicator trends in Iran and the eight selected Arab League countries. The results show that, based on the TOPSIS model, Iran ranked fifth among the countries studied in 2020 with a Ci value of 0.339, and second in 2024 with a Ci value of 0.452, representing the most significant development advancement with a three-rank improvement. This advancement was associated with increases in the weight of certain social (such as managed drinking water), economic (such as GDP per capita), and infrastructure indicators, although challenges such as rising greenhouse gas emissions and biological threats persist. The study highlights the need to strengthen environmental policies and design regional cooperation mechanisms to achieve sustainable development.