The aim of this study is to investigate fashion activism that supports sustainability by pursuing social transformation through social media. This is achieved by publicizing the environmental and labor problems of the fashion industry. For this study, a literary survey and netnography were conducted from January 2017 to November 2020. We classified and analyzed environmental and labor issues that could be considered fashion activism on social media. The results are as follows. First, movements for conscious consumption appeared as #haulternative, #fashionourfuture, #SecondHandSeptember, and #wornwear projects. These movements are concerned with buying used goods, re-dressing clothes owned by individuals, and transforming and wearing them with new methods. Second, activism for environmental protection includes #fashionOnclimate by Global Fashion Agenda and Sustainable Fashion Matterz’ #Watermatterz. These movements are directly involved in learning about the seriousness of environmental destruction caused by the fashion industry and participating in environmental protection with critical awareness. Third, the #whomademyclothes and the Clean Clothes Campaign are activism for improving the working environment, and are playing a role in publicizing labor issues by informing the general public about inadequate working conditions linked to the fashion industry. Thus, fashion activism on social media examined in this study can contribute to visualizing chronic problems that hinder sustainable development within the fashion industry.