"Redundant ad exposure", defined as simultaneous exposures to multiple exemplars of an ad, is an emerging ad exposure strategy on the Internet and has been employed increasingly by online news sites. The effects of such strategy, however, have never been examined. The current study took the initiative to examine the effects of redundant ad exposure strategy on brand memory and brand preference relative to two other commonly used online ad exposure strategies: single exposure and repeated exposure, when ad exposure was incidental. Additionally, the factor of ad size variation was included to test whether size variation interacted with ad exposure effects. In two experiments, a redundancy gain effect was revealed for exactly identical ads, but not for size-variation ads. Specifically, redundant exposures to exactly identical ads led to (a) greater brand memory and brand preference, as well as (b) faster response to choosing a preferred target brand, than single exposure. Redundant exposures to exactly identical ads were also (c) more effective than repeated exposures in many aspects. These findings provide implications and suggestions for media planners to rethink conventional and modern planning strategies with regard to incidental ad exposure on the Internet.