Introduction: This study investigated the role of working memory components (central executive, phonological loop, visual-spatial sketchpad) in mental addition of preschool female children. Method: 30 randomly selected preschool female students of elementary schools of Zanjan city with IQ ranges from 100 to 115 were tested by backward, forward and Corsi span tasks and mental addition problems (standard and nonstandard) that presented with verbal and non-verbal forms. Results: Statistics analysis by pearson correlation and regression methods showed a significant relation between backward span and performance in non-standard verbal problems and also between forward span and performance in standard verbal problems. There were no significant correlation between any of working memory components and non-verbal problems. Conclusion: Central executive is a good predictor of performance in mental addition specifically in non-standard verbal problems. In these problems, there are irrelevant information and annoying stimulus that must be inhibited. Central executive role in controlling attention and maximizing function is significant. However, in standard problems, there is no such request and only problems number and requests must be hold. In these problems, involvement of phonological loop is evident.