Objective To observe the color changes of nickel-titanium（Ni-Ti） orthodontic wires induced by fluoride. Methods Each 40 samples of 4 kinds of nickel-titanium orthodontic wires（IMD, SL, TP, YY） were put into artificial saliva with sodium fluoride at different F- concentrations （0.05%, 0.10%, 0.15%） and artificial saliva, separately. Dislodged the species and immersed them into artificial saliva with sodium fluoride for 3 minutes, then washed them with deionized water, and put back to artificial saliva, this course should be repeated 3 times per day. The whole immersion test lasted for 28 days. The color and micro-morphous changing were observed. Results The color changes came to be more serious as the F- concentration growing（P0.05）. Conclusion Fluoride can change the color of Ni-Ti wire. Different Ni-Ti wires get different changes at the same F- concentration.
