Fashion companies and brands’ marketing activities focus on resolving environmental problems; however, these companies’ efforts, there are some examples of so-called “greenwashing”. This paper aims to analyze different perceptions of brand authenticity, green marketing, and purchase intention toward the brand before and after exposure to case information about greenwashing. A total of 211 data were gathered and analyzed using SPSS 25.0. Respondents were asked to respond to same questionnaires related to green marketing and the brand authenticity before and after their exposure to greenwashing information. The study participants’ perceptions of green marketing from the brand were statistically significantly negatively changed after exposure compared to before exposure. Similar patterns in results were found in the context of consumers’ perception of brand authenticity (genuineness, originality, and consistency), and purchase intention. The originality of this study is in evaluating consumers’ perception of greenwashing focused on brand authenticity. The findings of the study suggest that if a fashion brand’s green marketing activity is perceived as greenwashing by consumers, the perceptions of green marketing, brand authenticity, and purchase intention can all decline. It is suggested that fashion brands need to develop a sincere and truthful green marketing campaigns to keep and enhance their brand authenticity.