Interactive media such as the Web have become a popular and important vehicle for communicating health information. However, little attention has been given to theorizing and empirically testing the effects of interactive media and the theoretical construct of interactivity. In this paper, we clearly identify and define the nature of interactivity examined. We then develop and test a theoretical model of website interactivity on information processing, involvement with communication, and attitude change in the context of stigma of mental illness. The results of an experiment revealed that interactivity of the website had positive main and moderating effects on dependent variables, while involvement with communication played a significant role in explaining the effects of interactivity. Implications for future research and for health communication campaigns for mental illness stigma are discussed.