This study examined the effect of message sidedness in public relations messages and its interaction effect with source credibility, in particular, with source trustworthiness and source goodwill, on the message recipients' attitude toward the message, the public relations issue, and toward the company. The findings provide a theoretical and practical background for public relations activities. In particular, this study highlights why it is important for a corporation to be perceived as a responsible corporate citizen by its target publics in its community, and how and when a company may use various types of message sidedness to make a public relations message more effective, depending on their perceived goodwill and trustworthiness among target publics. Finally, this study acknowledged the use of modern public relations tools by utilizing a weblog in the experiment.