Fast fashion brands seem to communicate their CSR activities via social media platforms, the effect of which can be explained through the attribution theory. Depending on whether the information received is negative or positive, this study aims to explore how consumers view and respond to fashion brands’ sustainability-related messages posted on social media. Data was collected by a survey company in the spring of 2018, and a total of 258 complete responses were used for data analysis. These findings suggest that when environmentally-conscious consumers evaluate communication through social media, they respond to both the perceived intrinsic and extrinsic motives of sustainability messages. Finally, this study recommends additional research on how to improve message content to make it more memorable, and therefore shared by the core consumers of fashion brands, to help improve all fashion brands’ overall communication efforts.