Social Economy institutions seek to provide answers to social problems, given that they naturally have a socially responsible mission. This study aims to answer the research question: how sustainable practices, namely environmental behaviour, have been adopted by Portuguese Private Social Solidarity Institutions (IPSS) with the purpose of contributing to Sustainable Development? To achieve this objective, qualitative research was carried out in 31 IPSS, which was framed within the scope of the TFA project (Theoretical framework for promotion of accountability in the social economy sector: the IPSS case). Semi-structured interviews were conducted, with a script based on the literature review, from May to July 2019, with those responsible for the management of these entities. A content analysis was conducted, using the NVivo12 Version 12.6.0 software, which enables data to be coded and categorised, reducing any researcher bias. The results indicate that most entities carry out activities of an environmental nature, related to the reuse of materials, the recycling of waste, the sale of materials for recycling, and user awareness. Several entities expressed financial limitations to the implementation of Environmental Management Systems and their accomplishment. However, the objections presented are not impossible to overcome, according to studies presented in other countries.