The fast fashion companies are growing with their cheap and trendy clothing, promoting people to adapt to new trends and to consume. At the same time, many fast fashion companies have started to advertise sustainable strategies which are communicated though social media. The aim of this research is therefore to investigate social media as a channel for fast fashion companies to communicate sustainable fashion advertisement, by looking at the Swedish market and the generation Y. A qualitative method was used, and the data was collected though semi-structed interviews. The conclusion of this study is that social media as a channel for fast fashion companies to communicate sustainable fashion advertisement, is not that effective, at least not how it is used to today. The sustainable advertisement on social media is not making the consumers of generation Y to purchase sustainable and the messages and content they communicate is not affecting generation Ys intention to purchase sustainable clothing. The communication from fast fashion companies regarding sustainable advertisements on social media should either be revised in order to meet the consumers demands, or to use another media channel to reach generation Y.