Heteronanojunction systems consisting of narrow gap semiconductors represented by metal sulfides and TiO(2) are highly expected as visible-light-active photocatalysts and the key materials for various photoelectrochemical devices. The common central issue is increasing efficiency of the light-induced interfacial electron transfer from the metal sulfide quantum dots (QDs) to TiO(2). We have newly developed simple and versatile low-temperature photodeposition techniques for directly coupling metal sulfide QDs and TiO(2) by taking advantage of its photocatalysis and the photoinduced surface superhydrophilicity. This critical review summarizes the recent developments in the photodeposition techniques and their unique characteristics. Subsequently to the Introduction, a theoretical view of the interfacial electron transfer is presented to obtain the guidelines for the design of the heteronanojunction systems. Then, the itemized description is given for the photodepositions of several kinds of metal sulfides on TiO(2) followed by the summary of the features of the photodeposition technique. Finally, the applications of the resulting heteronanojunction systems to the photocatalysts and QD-sensitized solar cells are described, and the excellent performances are discussed by relating with the features of the photodeposition technique (87 references).