Tin dichalcogenides of general formula SnSeyS2-y have been used as cathodic materials in test batteries having lithium and sodium anodes. The application of galvanostic intermittent titration and step potential electrochemical spectroscopy techniques allowed to distinguish two electrochemical steps during the discharge of the cells, irrespective of the alkali metal used as anode. The voltage-composition curves showed two successive domains with limits in the depth of discharge at ca. 0.3 and 1.0 F . mole(-1). X-ray data of discharged cathodes in the composition range 0.1 less than or equal to x less than or equal to 0.8/0.9 revealed the formation of a new phase, characterized by an expansion along the c-axis direction. Decomposition products such as Li2S or SnS were undetected. The diffusion coefficients of lithium and sodium obtained from galvanostatic and potentiostatic measurements showed a fairly goad agreement and were similar to those found in layer transition metal disulfides.