This study examines the effects of two types of consumer knowledge, product and brand knowledge, on consumer fit perceptions between an extension and its parent brand, so as to further investigate the role of consumer knowledge in brand extension evaluations. Based on the reviewed literature four hypotheses were proposed. The first two hypotheses predicted that both product and brand knowledge has an impact of consumer perceived fit between an extension and its parent brand. The other two hypotheses proposed that product knowledge affect more on the fit perceptions between a functional brand and its extension, while brand knowledge affect more on the fit perceptions between a prestige brand and its extension. An experiment was performed to examine these hypothesized relationships. Two hypotheses related to brand knowledge are supported, while the other two hypotheses related to product knowledge are not supported statistically. The results reveal that product and brand knowledge have different effects on consumer fit perceptions between an extension and its parent brand in terms of different brand types, functional vs. prestige brand. The experimental findings demonstrate that brand knowledge has an impact on consumer fit perceptions between an extension and its parent brand, and its effect dominant in prestige brand extension evaluations.