Abstarct: Marketing experts have described market segmentation as the cornerstone of modern marketing. Adopting segmentation helps corporations handle diverse customer needs and allocate resources effectively. The approach is lixnked to commercial success, encouraging organizations to pursue strategies that emphasize their strengths over competitors. Segmentation leads to more effective and better-targeted marketing programs. Market segmentation is widely used by most kinds of organizations in all sectors of the industry. This concept is at the heart of marketing strategy for corporations operating in both consumer and business markets. Market segmentation is the process of grouping similar consumers or business customers together in a market segment, in which the consumers or business customers exhibit similar requirements and buying characteristics. Organizations can succeed only if they are able to satisfy the needs of their customers. This involves providing suitable product and service combinations that satisfy these diverse needs. Customer satisfaction alone does not guarantee competitive success. Evidence suggests that successful organizations routinely use segmentation principles to guide their marketing strategy. Rough Set Theory was introduced by Pawlak in the early 1980’s. In the last quarter century it has become an important part of soft computing and has proved its relevance in many real-world applications. The rough set theory approximates a concept by three regions, namely, the positive, boundary and negative regions. Rules constructed from the three regions are associated with different actions and decisions, which immediately leads to the notion of three-way decision rules. A positive rule makes a decision of acceptance, a negative rule makes a decision of rejection, and a boundary rule makes a decision of abstaining. Using the concept created by Rough Set Theory and the three-way decision theory, the segmentation of different products of the company has been addressed. In this study, according to the customers' opinions and the likelihood of each product being purchased by them, product and customer segmentation has been investigated and the factors affecting product and customer segmentation have been extracted and the rules for selecting the most important market segments for investment have been determined.