ABSTRACT Background: Breast milk is important for brain development as it contains high concentration of long chain polyunsaturated fatty acids, also it contains cholesterol, amino acids as taurine and also lactose which broken to glucose and galactose, All are important nutrients for the brain and central nervous system tissues. Auditory Brainstem Response (ABR) is considered to reflect brain function of the infant and is widely used to determine/measure the brain development / maturation of the infant. Objective: to assess auditory brainstem maturation in breast-fed and formula fed infants as part of brain maturation using ABR. Methodology: thiscase-control was study carried out upon 100 apparently healthy infants; 50 infants of them were exclusively breast-fed and 50 infants were exclusively formula-fed, all of them aged 4-6 months. Each infant was subjected to detailed history, a full physical and neurological examination together with estimation of ABR. Results: There was statistically significant prolongation of absolute latencies of wave III and wave V of ABR of right and left ear in bottle feeding infants in comparison to breast feeding infants. Also, there was statistically significant increase of mean wave interpeak latencies I-III, III-V and I-V of right and left ear in bottle feeding infants compared to breast feeding infants. Conclusion: Better brain maturation in breast-fed infants compared to formula-fed infants evidenced by ABR.