Today, industrialization and technological developments have increased rapidly. Therefore, when evaluated in terms of countries, various problems such as population growth rate, global warming, pollution, environmental destruction, waste and air pollution have become more and more important issues. Countries need to take the necessary precautions and make some improvements in order to eliminate these problems and strengthen their environmental performance. Therefore, it is important to determine the environmental performance of countries. In this context, the aim of this study is to determine the environmental performance levels of the Organization for Economic Co-operation and Development (OECD) countries using ARAS (Additive Ratio Assessment) and WASPAS (Weighted Aggregates Sum Product Assessment) methods, which are among the Multi-Criteria Decision Making (MCDM) methods. The data used within the framework of this aim was obtained from the Environmental Performance Index (2022) Report. In order to determine the environmental performance levels of countries, 10 criteria have been determined: climate change mitigation, air quality, water quality, heavy metals, waste management, biodiversity, ecosystem services, acid rain, agriculture and water resources. These criteria have been weighted with the SD (Standard Deviation) method, and rankings have been made with ARAS and WASPAS methods. The ranking results obtained from both methods have been compared. According to the SD weighting method, the criterion with the highest weight is water quality, followed by air quality and acid rain criteria. In addition, according to the results of the analysis made with ARAS and WASPAS methods, the three countries with the highest level of environmental performance in the context of 38 countries included in the analysis are Sweden, Denmark and Finland, respectively.