This work reports the synthesis and characterization of a new efficient visible-light photocatalyst comprising SnO2 nanoparticles and cyclized polyacrylonitrile (CPAN). SnO2/CPAN nanocomposite was synthesized through two steps: first, adsorption of polyacrylonitrile (PAN) in N,N-Dimethylformamide solution by SnO2 nanoparticles to form SnO2/PAN nanocomposite; second, cyclization of PAN in the SnO2/PAN nanocomposite by heating at 250 degrees C for 2 h. The characterization by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, N-2 adsorption-desorption curves, and UV-vis diffuse reflection spectra indicated the synthesis of large surface area SnO2/CPAN nanocomposite with remarkable visible-light-harvesting ability. SnO2/CPAN nanocomposite exhibited exceptionally high photo catalytic activity in the reduction of aqueous Cr(VI) under visible-light (lambda > 420 nm) irradiation (the reaction rate constant of photocatalytic reduction of Cr(VI) by SnO2/CPAN is about 16.6 times that by SnO2). The possible mechanism for the high visible-light-driven photocatalytic activity of SnO2/CPAN nanocomposite was proposed.