A field experiment was conducted to investigate the effectiveness of a persuasive strategy—partial incongruity strategy—in enhancing the persuasiveness of low prestige sources. Two hundred and two subjects from a major city in New England participated in the study. Through the manipulation of various versions of specially designed messages, the researcher examined the effectiveness of the partial incongruity strategy in inducing message acceptance among subjects holding different initial attitudes on an issue. In addition to the audience's pre-existing attitude, audience's self-perception of knowledge ability on the issue was also examined as a component of the individual’s predisposition which served to indicate the intensity of the pre-existing attitude. Results from the analyses support the hypothesis that the use of "partial incongruity strategy" did enhance the persuasiveness of a communication attributed to a low prestige source. In addition, the study also suggests that the persuasive strategy will work most effectively when the following two conditions are met: (1) the "partial incongruity" portion presented in the message must produce a sufficiently large discrepancy between the message and the source so as to create an impression of "unselfishness," and to win over the audience’s trust; and (2) the audiences must not hold an extremely opposing position on the issue.