The main reason for investigating the effects of sustainability activities on firm performance is to determine whether sufficient sustainability activities have an impact on inreasing financial performance or insufficient sustainability activities have an impact on decreasing financial performance. Findings that sustainability activities are rewarded in terms of performance will be a motivating factor for the sustainability studies of both the private and public sectors. This study investigates the effect of inclusion in the Borsa Istanbul (BIST) Sustainability Index on corporate financial performance for the period 2015-2017. In order to control the unobserved firm heterogeneity, panel data methods model is applied. The results show that the effect of inclusion in the sustainability index on corporate financial performance is not statistically significant.