Customer Satisfaction is a major concern for all the firms, therefore building customer royalty and trust is the key factor to succeed in todays severe competition on the marketplace. To give satisfaction, understanding the existing customers needs such as focusing on how to sell a product to enhance customer retention and reduce the number of dissatisfaction become a critical issue than attracting new customers. The main purpose of this study is to present the methodology to understand customer characteristics classified by department stores customer grade and RFM (Recency, Frequency, monetary) customer grade. Then, by using decision tree technique and various statistics methods, we present a new marketing strategy to retain customer royalty.