The relationship between strategic similarity and performance is an important issue in the field of strategic research. Various theories have directly or indirectly discussed this issue. This study synthesizes relevant theories and investigates empirically similarities of promotion strategies among three supermarket stores in Kaoshiung area. It shows that there exists inverse-U shaped relationship between strategic behavioral similarity and adjusted sales. Adjusted sales are lower in the situations of extremely high similarities and extremely high dissimilarities and are higher in the situation of moderate similarities. Based on the empirical results, this study discusses the validity scope of each theory and indicates the implications of adopting differentiation and imitation strategies.