The chemical states of Bi in BiI3-nylon 11 nanocomposites during X-ray irradiation were investigated by X-ray photoelectron spectroscopy (XPS). It has been found that with prolonging exposure to soft X-rays, Bi 4f peak of Bi metallic state emerged at lower binding energy side and the peak intensity continuously increased, while Bi 4f peak intensity of BiI3 gradually decreased. The valence band spectra of BiI3-nylon 11 nanocomposites show that the density of states near Fermi level increases with increasing the X-ray irradiation time due to the formation of metallic Bi, which is favorable to the conductivity. Besides, we have observed that BiI3-nylon 11 nanocomposites show a new photochromic effect, changing color from orange-red to black after prolonged exposure to the soft X-rays. The color turns to orange-red after air exposure. It has been found that the color change is intimately related to redox behavior of Bi atoms in BiI3-nylon 11 nanocomposites. We have also observed that the XPS charging shift and the resistance of BiI3-nylon 11 nanocomposites decrease with increasing X-ray exposure time. This phenomenon may be used to inspect the X-ray photoconductivity preliminary. (C) 2010 Elsevier B.V. All rights reserved.