The present study investigated the effects of communication styles, source expertise, and audiences’ preexisting attitudes in the contexts of the debate regarding genetically modified organisms. A between-subject experiment ( N = 416) was conducted manipulating communication styles (aggressive vs. polite) and the expertise of the communicator (scientist vs. nonscientist) in blog articles. The results showed significant effects of communicator expertise and individuals’ preexisting attitudes on writer likability and message quality, depending on the communication style used. Expectancy violation was found as a significant mediator that explains the differences. These findings provided a plausible explanation for the way in which communication styles work in science communication contexts and offered practical implications for science communicators to communicate more strategically.