In order to prevent fluoride toxicity, the dietary fluoride intake should be considered before giving the fluoride supplement to the high caries risk children group. At present the consumption of ready-to-drink 100% fruit juice in Thai children have increased dramatically. Objective: The objective of this study was to determine the fluoride pH and content in ready-to-drink 100% fruit juice sold in Bangkok. Methods: Fourteen types of ready-to-drink 100% fruit juice (N=140) were used. 2 ml of filtered fruit juice was mixed with 0.2 ml of TISAB III. Then the fluoride concentration in the solution was measured with the Fluoride electrode (Orion model 96-04, 96-09) connected to the Ion Analyser (Orion model 940, Orion, USA). Results: The means pH and ± standard deviation of popular fruit juice in Bangkok ranged from 3.00±0.089 (guava juice) to 3.75±0.060 (Valencia orange). The lowest mean of fluoride content was 0.019±0.002 ppm found in guava juice. The highest mean of fluoride content was 1.064±0.007 ppm found in red grape juice. The mean fluoride content of orange juice, apple juice and red grape juice ranged from 0.021±0.003 ppm to 0.589±0.029 ppm, 0.194±0.008 ppm to 0.728±0.004 ppm and 0.0441±0.010 ppm to 1.064±0.007 ppm, respectively. Conclusions: It was concluded that the fluoride content in ready-to-drink 100% fruit juice should also be considered in addition to the fluoride concentration of the drinking water before fluoride supplementation. Supported by the Faculty of Dentistry, Mahidol University.