Financial markets can play a role in sustaiability development. They can support sustainability by making ESG disclosure, launching sustainability related indices or offering sustainability guidance for listing companies. All of these activities helps in developing sustainability. This article is an attempt to analyze sustainability support level in stock exchanges in the world. It is based on a survey conducted in 27 stock exchanges. The aim of this article is to assess the level of stock exchanges sustainability support and examine the relationship between the stock market size and sustainability support level. To acheve the aim the assessment tool has been created. Sustainability Support Index is a synthetic stock markets sustainability support measure. It helps to compare stock exchange sustainability support levels. In the article statistical tools are used to compare the phenomena, mainly regression analysis and Pearson’s correlation. The conclusion presented in the article states that there is a differential stock market sustainability support level in the world. There is no clear correlation between sustainability support variables and stock market size variables.