Tungstosilicates (SiWA), acting as target molecules, were entrapped into MAAM/VTEOS/TEOS hybrid matrix by combining self-assembly technique and sol-gel process. The hybrid film was obtained by spin coating process and was characterized by IR, XRD and TG-DSC. Its photochromic behavior and mechanism were also studied by UV-vis and ESR spectrometries. The results show that SiWA still maintain Keggin structure in the matrix, interacted with -NH2 group of matrix through hydrogen bond. After UV irradiation, W6+ is reduced to W5+ due to ligand-to-metal charge transfer (LMCT) and a free radical is formed at the same time. The decoloration process is closely related to the presence of 0,. The hybrid film exhibits an excellent photochromism, mechanical strength and thermodynamic stability. (c) 2005 Elsevier B.V. All rights reserved.