Abstarct: Today, companies are trying to study the behavior of consumers, to attract their trust. This trust can be strengthened by creating brand value in customers' minds. In other words, it influences on consumers' purchasing behavior through the value that brands can create in the customers’ minds. Thus, this Study intends to evaluate consumers’ behavior with regard to brand value and perceptual error using fuzzy Rough set theory. The type of study is an applied research in the terms of goal and survey research in the terms of methodology. In this context, the sample of 385 consumers of Clear and Sedr-e-Sehhat shampoos, are studied which eventually, 11 rules have been selected to further investigating. The results show that “trade leverage”, “availability” and “consideration of brand”, “creating positive attitude” are more important than the others in the terms of “purchasing performance”. Moreover, in the terms of “Recommending to the others”, “new customer attraction”, “being different compared to other competitors”, “depending on the brand” and “creating positive feelings” are the most important factors. Finally, baxsed on the dimensions removed, creating the perceptual error in some aspects has been set.