Improving ad effectiveness and reducing ad intrusiveness are essential issues for online advertising. The study examines how video viewers' cognitive absorption is affected based on theories regarding cognitive absorption, cognitive engagement and flow. Furthermore, this study examines how cognitive absorption relates to ad intrusiveness, irritation and avoidance. We posit that video viewers' cognitive processing is enhanced when they are highly absorbed in the video content, and that when their viewing is interrupted by an ad, their perception of the ad's intrusiveness increases. A laboratory experiment is conducted to examine the proposed research model. The research findings can help advertisers and ad service providers understand when to deliver intrusive video ads while minimizing the viewer's negative reactions.