|Individuals and organizations consume the world’s underground and ground resources for their own needs and desires, and this situation destroys the continuity and sustainability of future generations and the world. Governments and companies are the most responsible actors in turning this situation from a possibility into a reality. For this reason, the idea and practices of limiting the environmental and social impacts of the activities of all economic units, whether government or company, are becoming increasingly important. The Sustainability Index includes companies that trade on the Borsa Istanbul (BIST) and have a high level of sustainability performance. Every year, the companies in the index voluntarily report their sustainability-related activities to the public through “sustainability reports”. The practices and explanations of environmental sustainability were investigated in this study by looking at the sustainability reports of 38 firms in the BIST Sustainability Index during the 2018–2019 and 2020 – 2021 periods. According to the results of the content analysis on the use of 41 environmental statements; in both periods, environment and climate were the most used expressions. While soil pollution, visual pollution and noise pollution in the 2018 – 2019 period and waste control, soil pollution in the 2020 – 2021 period were the least used expressions, environmental inspection and green finance were not included at all in the same period. In addition, in both periods, on a sectoral basis, holding and investment companies and banks have the highest number of expressions, while informatics and defence have the least. The comparison revealed that expressions were used more frequently overall, their relevance and frequency altered throughout time, and some were never used again in the subsequent period.