Molten salt chemistry of chalcogenides has become a major concern in relation to two current great application domains which are (i) nuclear energy (pyrochemical nuclear waste treatment and molten salt reactors) and (ii) electrodeposition of functional material thin films (photovoltaic, magnetism, supraconductivity, etc.). This paper reports experimental data relevant to the molten salt chemistry of selenium in the molten LiCl-KCl eutectic for temperatures ranging from 450 to 600 degreesC. In fact, it is intended to use selenium to obtain electrodeposited thin films of semi-conducting materials (such as ZnSe) by co-reduction of Se(IV) and Zn(II). Performing chemical oxo-acidobasic titrations of a strong oxide donor (Li2CO3) with selenium dioxide, it was possible to determine the nature of the stable and soluble species of selenium in the melt: SeO2 Cl-2(-), SeO2- and Se2O76-. Analysis of experimental data allows us to determine the respective stability dissociation constants of these species as a function of temperature. Merging the resulting data with available thermochemical data allowed us to construct the molten salt chemistry in the form of potential-oxo-acidity diagrams. (C) 2004 Elsevier B.V. All rights reserved.