This experiment explored how consumers evaluate electronic word-of-mouth (eWOM) messages about products. Each participant was exposed a 10-message set in a single board. Five groups were manipulated in terms of their ratios of positive and negative messages. The result showed significant differences across various sets of eWOM messages. Although more positive sets showed higher scores in many cases, this was not true in all situations, especially for the case of credibility. Involvement and prior knowledge partially moderated the relationship between the ratio of messages and the eWOM effect. The credibility of Web sites and eWOM messages can be damaged in the long run if all of the eWOM messages are positive.