The aim of this study was to investigate the electrochemical behavior of strained commercially pure (CP) titanium in slightly acidic fluoride-containing media by electrochemical impedance spectroscopy (EIS) measurement. The electrolyte chosen in this study was 1% NaCl solution with different NaF concentrations ranging from 0 to 1%, at pH 6 and 37 8C. Different tensile strains, including 0, 1, 2, 4, 5 and 10%, were applied to the test specimens with a tensile testing machine during the EIS measurements. Surface chemical analyses were performed with electron spectroscopy for chemical analysis (ESCA) and Auger electron spectroscopy (AES). The results showed that the impedance decreased with increasing the NaF concentration and the tensile strain. When the NaF concentration was higher than 0.1%, the protectiveness of TiO2 formed on CP titanium was destroyed by fluoride ions, resulting in the formation of a complex compound of Na2TiF6, regardless of the tensile strain applied. According to the surface chemical analyses, the equivalent circuits simulating the electrochemical behavior of strained CP titanium in slightly acidic media with different NaF concentrations were proposed.