The present investigation examined the sexual dimorphic patterns of cardiorespiratory fitness to working memory in preadolescent children (age range: 7.7-10.9). Data were collected in three separate studies (Study 1: n = 97, 42 females; Study 2: n = 95, 45 females; Study 3: n = 84, 37 females). All participants completed a cardiorespiratory fitness assessment in addition to a specific measure of working memory (i.e. the operation span task, the n-back task, or the Sternberg task). Results from all three samples revealed that higher cardiorespiratory fitness levels were associated with better working memory performance only for males with no such relation observed for females. In addition, the sexually dimorphic pattern was selective for the most challenging working memory conditions in each task. Together, these findings reveal new evidence that cardiorespiratory fitness is selectively related to better working memory performance for male children. This investigation provides additional insight into how interventions aimed at improving fitness may influence cognitive development differentially among preadolescent children.