ABSTRACT The purpose of this study is to identify how sustainable fashion brands communicate with consumers on social media, specifically, Instagram. By applying a data mining technique to analyze brand posts and consumer comments, we thoroughly examine how consumers engage with sustainable messages from each brand and how those engagements are associated with brand posts. A sample of six sustainable fashion brands was selected, including Eileen Fisher, Everlane, Girlfriend Collective, Patagonia, Reformation, and Stella McCartney. Public posts of the six brands and corresponding consumer comments on Instagram between November 1, 2019 and November 1, 2022 were collected. LDA (Latent Dirichlet Allocation) text mining technique was applied to extract topics from each brand’s posts and follower comments. A fixed effects linear panel model was then employed to examine if consumer comments are significantly associated with sustainable messages from each brand. Ten major sustainability-related themes were identified from brand posts, and four major sustainability-related themes were discovered from consumer comments. The linear panel results provide preliminary evidence that the sustainability-related themes from consumer comments are positively influenced by the sustainability-related themes from brand posts, indicating that brand posts indeed affect consumers’ opinions about sustainability.