Mg2Sn based thermoelectric (TE) materials were prepared by a low-temperature solid-state reaction between MgH2 and Sn. Reaction between tin and magnesium hydride instead of pure magnesium minimizes the oxidation and volatilization of magnesium. The thermoelectric performance was measured over the temperature range 300~750 K. All samples indicate n-type conduction within the whole temperature region, while they show a tendency to be nearly p-type with the temperature increasing. The Seebeck coefficient of Y-doped Mg2Sn has been enhanced, and the power factor has been 40% higher than the value of reference. The 0.2% Y-doped Mg2Sn exhibits a maximum figure of merit ZT of 0.033 at 350 K, which is nearly 3 times of the value of reference.