Website usability is a widespread study area which incorporates researches from various disciplines. Several methods are available to evaluate usability of a website. Checklists, heuristic evaluations, expert evaluations, surveys and user tests are presented as the most popular methods for the evaluation of websites. Especially ecommerce websites' usability has a critical importance due to the rising in competence and the rising in the number of e-commerce websites. The diversity of e-commerce

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... ebsites evokes typical example of multi criteria decision making (MCDM) issue in daily life of humanity. Since different user groups have different expectations from the websites, the evaluation method should be structured to include appropriate measurement criteria. The main aim and the target users of the website should be considered attentively while defining the evaluation method. In this study, the most visited (Based on Alexa.com list in January, 2018) e -commerce websites in Turkey are compared in terms of usability. Criteria are decided based on the study which was published by Lee and Kozar (2015). Two different weighting approaches are integrated to TOPSIS method. One of these approaches is fuzzy expert evaluation and the other one is weighted regression est imate. We aim to discover different impressions between e-commerce website designers and users on the same criteria to provide a comprehensive viewpoint.