A novel colorimetric and ratiometric probe (SH-GA) for the fluoride ion detection was designed and synthesized from gallic acid. SH-GA exhibited a selective color change from colorless to yellow in the presence of F⁻ among the eight anions (F⁻, Cl⁻, Br⁻, I⁻, H₂PO₄⁻, HSO₄⁻, CH₃COO⁻, and ClO₄⁻), either in THF or DMF solutions. The binding stoichiometry between SH-GA and fluoride ions was determined to be 1 : 1, and the complexation constant was 1.5 × 10³ M⁻¹ in THF. The detection limit of the SH-GA probe reached as low as around 1 μM in THF. ¹H NMR titration results and DFT calculations suggested a deprotonation process via hydrogen bonding interactions between the fluoride ion and amino group of SH-GA.