[en] Persistent Photoconductivity (PPC) in hydorogen-ion implanted (001) oriented KNbO₃ bulk single crystals (perovskite structure at room temperature; ferroelectric with a band gap of 3.16 eV) is studied in air at room temperature to prevent the crystallinity degradation caused by the phase transition. Hydrogen is implanted into KNbO₃ bulk single crystals using the energy (the peak ion fluence) of 500 keV (5.0 × 10¹⁵ cm^-2). The resistivity varies from ∼10⁸ Ω/□ for an un-implanted KNbO₃ sample to 2.3 × 10⁵ Ω/□ for as-implanted one. suggesting the presence of donors consisting of hydrogen interstitial and oxygen vacancy. The PPC is clearly observed with ultraviolet and blue LEDs illumination rather than green and infrared, suggesting the release of electrons from the metastable conductive state below the conduction band relating to the charge states of the oxygen vacancy as observed in electron irradiated ZnO. (paper)