Surface modification may significantly improve the performance of thermoelectric materials by suppressing thermal conductivity. Using the powder atomic layer deposition method, the newly developed Sb2O5 thin films produced from SbCl5 and H2O2 were formed on the surfaces of Bi powders. Because of the high thermal resistance generated by Sb2O5 layers on Bi particles, a substantial decrease in κtot from 7.8 to 5.7 W m-1 K-1 was obtained with just 5 cycles of Sb2O5 layer deposition and a 16% reduction in κlat. Because of the strong phonon scattering, the maximum zT values increased by around 12% and were relocated to 423 K.