Novel I-doped Bi12O17Cl2 photocatalysts have been synthesized using a facile chemical precipitation method and characterized by XRD, XPS, SEM, BET and UV-vis DRS etc. The corresponding results indicate that I- ions enter into the crystal lattices of Bi12O17Cl2 and replace partial Cl- ions. In addition, the doped I- ions form an impurity level over valence band and extend the visible light absorption ranges of Bi12O17Cl2. I-doped Bi12O17Cl2 exhibits much superior visible-light (lambda > 420 nm) photocatalytic activity to that of the pure Bi12O17Cl2 in the methyl orange (MO) and phenol degradation, because a little amount of I- ions can boost the photocharges separation efficiency, which is ensured by photoluminescence spectra, transient photocurrent responses and electrochemical impedance spectra. It is expected that this work opens a new potential pathway to improve the photocatalytic activity of non-stoichiometric ratios bismuth oxyhalide via ions doping strategy.