Background: Breastfeeding has been widely researched and reviewed in relation to cognitive performance in children, but early reviews have not provided compelling evidence linking breastfeeding to cognitive development Objective: To assess the effect of breastfeeding duration and exclusivity on the cognitive development of a group of preschool Egyptian children. Methods: The current study was a cross sectional comparative study that included 90 apparently healthy preschool Egyptian children aged 3 - <6 years who were classified into three equal groups according to their type of feeding in early infancy. Assessment of neurocognitive function and IQ was done using the following 3 tests: Stanford-Binet test 5th edition Arabic version (2003), Kaufman Assessment Battery for Children (2004), Illinois Test of Psycholinguistic Abilities (ITPA) (2001). Results: There was significant increase in IQ detected by kauffaman test in breastfed group than either mixed or artificially fed, while no significant difference was found in IQ between mixed and artificial fed groups. There was significant increase in psycholinguistic age in breastfed group in comparison to artificially fed groups, while no significant difference was found between breastfed and mixed fed or mixed fed and artificially fed groups. Children who were breastfed had better scores in Total IQ than either artificially or mixed fed. Also, there was significant increase in total IQ scores in mixed than artificially fed groups. A significant positive relation was found between the total duration of breastfeeding and Binet total IQ score. Conclusion: The effect of breastfeeding is dose-dependent, the longer the duration of breastfeeding, the more is the benefit, the strongest effect for cognitive function in breastfed children was more prominent in psycholinguistic age.