Metaphors are used frequently in advertising. They invite elaboration, bring in the pleasure of interpretation, and suppress the occurrence of counter arguments. However, thus far, we still lack evidences about whether these features actually make an advertisement more persuasive, and whether the persuasiveness of a metaphoric ad is influenced by advertiser credibility. This study manipulates metaphor and advertiser credibility in an experiment, and observes Attitude toward the Ad (Aad), Attitude toward the Brand (AB) and recommendation intention. The results indicate that metaphors increase the effectiveness of ads. The persuasiveness of metaphor ads varies with advertiser credibility; metaphors used by high credible advertiser produce more favorable Aad and AB than low credible one. In addition, the extent of increase in persuasiveness is the same for high and low credible advertisers.