Mn and Co doped Fe2Si5 based thermoelectric alloys were prepared by melt-spinning technique. XRD analysis showed that only alpha phase existed in the as-solidified Fe2Si5 based alloys, and semiconducting beta-FeSi2 thermoelectric phase and silicon were formed by the eutectoid decomposition of alpha phase during annealing other than the peritectoid reaction. Thermoelectric properties measurement suggested that a number of grain boundaries, which were created by rapid solidification process, enhanced carrier scattering and hence increased the Seebeck coefficient and electrical resistivity of Fe2Si5 alloys. Co doped samples had the higher power factors than those with the same amount of Mn dopants because the higher carrier concentrations could be obtained.