Sustaining competitive advantage is one of the most concerns of companies in order to compete with rivals for attract new customers and keep the existence. Several strategies to keep advantages were in object in different segments and different marketplace. Companies are trying to work on strategies with proper drivers and resources to sustain advantages. One of these drivers is service quality which was a determinant factor for customers and their perception about different firms. With increased portion of Internet in business, all these discussions shift in to the cyber space. In other words, firms are trying to sustain competitive advantage on the Internet through different ways. Delivering E-service to the customers, E-service quality and its dimensions is of importance to customers and decision makers. In this study, we discuss about terms of strategies which firms can sustain competitive advantage especially through the Internet and then discuss about service and e-service quality aspects and dimensions to answer our research question: what is the influence of e-service quality on sustaining competitive advantage for firms? We have generalized five hypotheses for this agenda after extracting proper factors for e-service quality in frame of reference. Then we have used deductive approach to this survey and applied quantitative data collection to distribute our questionnaire among our samples which consists of Iranian IT firms segment. After collecting data, evaluating validity and reliability of statistical analysis is going to perform to find the impact of e-service quality on sustaining competitive advantage e. Finally based on results from data analysis, we will find a significant relation and influence between e-service quality of Iranian IT firms and sustainability of their advantage through the rivals which this results indicate that in Iran's e-marketplace (as a developing country) firms can be differentiated from each other easily through superior e-service quality which they offer.Validerat; 20111116 (anonymous