Abstract :Nowadays, firms cannot have enough competitive power with the goal of profit maximiza- tion. Firms that consider social utilities, invest in the future, fulfill their social responsibi- lities and adopt corporate governance principles and focus on sustainability can reach real success. The whole of these criteria constitutes the concept of “corporate sustainability”. The BIST Sustainability Index (XUSRD), which started to be calculated in 2014, is to inc- rease the sustainability practices among firms by creating a platform, which includes firms trade on the Borsa Istanbul and having high corporate sustainability performances. From this point of view, it is aimed to compare the financial efficiencies of the firms before and after taking part in the XUSRD. For this purpose, financial efficiencies of the firms were measured by Data Envelopment Analysis (DEA) and Malmquist Index values were calcu- lated for comparison in the time dimension. As a result, it was determined that firms have higher levels of efficiency after taking part in the XUSRD. Keywords : Financial Efficiency, Corporate Sustainability, BIST Sustainability Index, Data Envelopment Analysis, Malmquist Index
