Gaining brand loyalty is an ongoing marketing challenge for online companies. We’re interested in whether there is a relationship between brand loyalty and customer concentrations so that it can provide a new perspective to e-commerce websites for the understanding of customer behaviors and make suitable marketing strategies. Using the comScore database for year 2006 and year 2007, we first apply the Inverted Lorenz Curve method to calculate the customer concentrations of purchase amount, purchase frequency, pages viewed, visit frequency and duration. Furthermore, brand loyalty indexes with respect to above purchase and search propensities are calculated by taking the aggregate average of individual’s brand loyalty. We then run regression analysis using customer concentration and a dummy variable as independent variables, and brand loyalty index as the dependent variable. From the empirical results, major findings are as followed: Customer concentrations in terms of search propensity of visit frequency and duration show POSITIVE association with brand loyalty. In contrast, customer concentrations in terms of purchase propensity of purchase frequency and search propensity of pages viewed show NEGATIVE association with brand loyalty. And there is no apparent association in purchase propensity of purchase amount. In addition, from the results of regression analysis with respect to different purchase and search propensities, the marketers are able to identify the target customer groups and assign priority in regarding to raising brand loyalty. Finally, it might be strategically wise to keep track of own company and its competitors’ changes or trends in customer concentration and brand loyalty index with respect to purchase and search propensity of purchase amount, purchase frequency, pages viewed, visit frequency, and duration, respectively.