Composite fine particles such as ZnO-TiO2, CdS-TiO2, ZnS-TiO2 and Ag-TiO2 were prepared by ultrasonic spray pyrolysis of metal salt aqueous solution in which TiO2 (Degussa P25) particles were suspended. The crystallinity, chemical compositions, and morphologies of the produced particles were investigated by XRD, centrifugal particle size analyzer, and SEM/EDAX. The photocatalytic activity of the modified particles was investigated for the decomposition of trichloroethylene (TCE). The prepared particles were micro-porous and had spherical shapes of 0.3-1.5 mu m in diameter. The size and size distribution of the prepared particles were not significantly changed by the type and loading of modifier. The crystallinity and crystallite size of TiO2 was not changed by these modifications. The photocatalytic activities of modified particles was slightly higher than pure titania when the loading was low. However, as the loading was further increased, the photocatalytic activity was sharply decreased and became almost constant. (C) 1999 Kluwer Academic Publishers.