Since online advertisements (ads) can be presented in various forms, a critical issue for advertisers is to determine how to maximize advertising effects through appropriate design. Factors involved include how the ads are presented to forcibly catch the attention of consumers and the congruity of themes between the ad and Web page contents. Both affect whether the ads can generate positive feedback in the online advertising environment. This research, through laboratory experiment design, tries to investigate the influence of forced ad exposure on advertising effectiveness, with congruity being an important moderator. Results show that congruity is especially important for pop-up ads and that forced ad exposure affect memory effects if the moderating effect of congruity is excluded from the model. Discussions, managerial implications, suggestions for future research, as well as limitations of this study are addressed.