Although social marketing promotion efforts are typically evaluated online using either finished video or static images, limited evidence exists whether media type influences audience response. In a posttest-only experimental study with a nationally representative sample of 663 Canadian mothers of 5- to 11-year-old children, participants were randomly assigned to one of two media conditions consisting of Think Again physical-activity Public Service Announcements created by ParticipACTION. Mothers reported campaign recall, ad liking, motivation to respond to the ad (i.e., assist one’s child to get at least 60 min of physical activity every day), and their support behaviors. Data were analyzed using χ2 and independent samples t-tests. Those exposed to the video version of the ad in comparison to the static image reported higher message recall and liking, and motivation to respond. There were no differences in parental support behaviors. Social marketing promotion efforts should be evaluated using the same format as the media message originally used. The study concludes that media type influences findings when evaluating social marketing promotion campaigns.