Purpose: To determine the optimal electric current intensity of fluoride iontophoresis (FI) for remineralisation of early caries lesions in vitro. Materials and Methods: Sixty specimens were made from bovine incisors and immersed in a demineralising gel for 96 h. Specimens were divided into control (conventional fluoride application) and experimental (FI) groups. All of the specimens were covered with fluoride for 4 min every day. Different electric current intensities (100, 200, 300 and 400 μA) were applied in the FI groups using the FI device. The concentration of KOH-soluble fluoride was determined to evaluate the amount of CaF2 formed on the tooth surface. The reduction in lesion depth was measured by polarised light microscopy. Results: The concentration of KOH-soluble fluoride was the highest in the specimens of the 300 μA FI group. However, there was no significant difference in the reduction of lesion depth between the experimental groups and the control group. Conclusion: Variations in the electric current intensity influenced the amount of CaF2 formed on the enamel surface, with the greatest amount found for 300 μA. Keywords: early caries lesion, electric current fluoride iontophoresis, remineralisation