This research examines the interplay between brand structure (i.e., cohesiveness and similarity) and extension typicality on extension spillover effects using two experimental studies. The results reveal that the dominance of brand similarity and cohesiveness on extension spillover effects depends on how typical the effecting brand extension is to its brand. For typical extensions, the cohesiveness of existing brand extensions is the determinant factor on extension spillover effects. In contrast, for atypical extensions, the similarity of existing brand extensions is the determinant factor on extension spillover effects. Moreover, brands with similar brand extensions are inherently perceived as high cohesive brands, which enhance perceived brand quality. In contrast, brands with dissimilar brand extensions are inherently perceived as low cohesive brands, which weaken perceived brand quality. However, brands with dissimilar brand extensions are perceived to be cohesive brands if the product functions of the brand extensions are interdependent.