Practitioners and academics are eager on measuring service quality accurately in order to have better understanding of its indispensable antecedent and consequences, and eventually ascertain methods for improving and measuring service quality in search for competitive advantage. The aim of this study is to rank the dimensions of service quality that affect the customerspsila expectation in online purchasing in Iran from the customerspsila perspective. A questionnaire used in this study was published in Cloob.com which is an Iranian virtual society Web site. The measurements used were based on the widely accepted SERVQUAL model which is the most common method for measuring service quality. This study also examined the service quality gap by comparing customerspsila expectations and their actual perceptions. The results of the study indicated that all of the service quality factors are important. Tangibility was rated as the most important dimension followed by assurance, reliability, responsiveness, and empathy.