Introduction: Fluoride exists naturally in water sources and is derived from fluorine. It is well known that fluoride helps, prevent and even reverse the early stages of tooth decay.   Aim: The aim of the present study was to determine the fluoride levels in plasma and breast milk of lactating mothers in Egypt (Cairo and Giza Governorate).   Material and Methods: Two hundred healthy lactating mothers aged between 20-40 years old were asked to give plasma and milk samples voluntary. Breast milk samples were directly refrigerated until measurements. The fluoride concentrations of plasma, milk and drinking tap water were assessed using an ion-selective fluoride electrode combined with an ion analyzer.   Results: The fluoride levels of plasma, breast milk and drinking tap water samples were 0.0207±0.012,0.0111±0.0044 ppm, and 0.482±0.117 ppm, respectively. A significant direct correlation between fluoride content in breast milk and drinking tap water was found (r=0.858, p< 0.01).