Purpose This study aims to investigate the international portfolio diversification opportunities provided by Turkish sustainable firms to international socially responsible investors. Design/methodology/approach The Borsa Istanbul Sustainability Index (XUSRD) and FTSE4Good index family daily data for the period of 11/04/2014-12/31/2017 is used and the DCC-GARCH model is applied to explore the dynamic correlation linkages. Findings The results indicate that co-movements between XUSRD and FTSE4Good indices are time-varying and generally display a low level. While the highest average conditional correlation value was observed between XUSRD and Developed 100 index, the lowest one was between XUSRD and FTSE4Good Japan index.