A chalcogen-containing compound of the following Chemical Formula 1 which exhibits excellent phase stability at a low temperature, particularly at a temperature corresponding to the driving temperature of a thermoelectric element, and also exhibits an excellent thermoelectric performance index through an increase in a power factor and a decrease in thermal conductivity, a method for preparing the same, and a thermoelectric element including the same: V1-xMxSn4Bi2Se7-yTey  [Chemical Formula 1] In the above Formula 1, V is a vacancy, M is an alkali metal, x is greater than 0 and less than 1, and y is greater than 0 and less than or equal to 1.