Business to Business (B2B) e-commerce has become increasingly important in e-commerce. However there is little research on the definition and evaluation of user satisfaction with B2B website. Traditional scales, like User Information Satisfaction (UIS), End-User Computer Satisfaction (EUCS) and Customer Information Satisfaction (CIS) focus on the individual users of Information System (IS) and are not suitable to the B2B business environment. In this article, we establishe a scale of "B2B Ecommerce Website Customer Satisfaction" (B2B-ECWCS) with five dimensions and highlight the significant factors in the B2B-ECWCS scale. We then present the results of testing and validating the scale with customer data of Alibaba, the largest B2B business in China.