Preparation methods for TiO2/PbS "coupled" type nanoparticles are described, in which PbS is formed in-situ on the surface of TiO2. FTIR was used to follow the preparation process and UV-vis spectra confirmed the stabilizing effect of TiO2 on the formation of PbS nanoparticles. This "coupled" type of nanoparticle was further assembled into ultrathin composite films based on electrostatic interaction as the driving force. Various methods, including UV-vis, IR, EDS, TEM, AFM, and XBS, identified the coexistence of two kinds of nanoparticles in ultrathin composite films. Photocurrent measurements indicated that efficient charge transfer occurred in the composite films.