Ag-dispersed Bi0.5Sb1.5Te3 was prepared successfully by silver acetate (AgOAc) decomposition and hot pressing. The Ag nanoparticles were well-dispersed in the Bi0.5Sb1.5Te3 matrix, and acted as phonon scattering centers effectively. The electrical conductivity increased systematically with increasing amount of Ag nanoparticle dispersion, whereas it decreased with increasing temperature similar to metals or degenerate semiconductors. All specimens had a positive Seebeck coefficient, which confirmed that the electrical charge was transported mainly by holes. The Seebeck coefficient of Bi0.5Sb1.5Te3 decreased with increasing temperature but its temperature dependence was changed by Ag dispersion. The power factor values for Ag-dispersed Bi0.5Sb1.5Te3 increased significantly due to the increase in effective carrier mass and were higher over the entire temperature range. The decrease in lattice thermal conductivity by Ag dispersion overcame the increase in electronic thermal conductivity. The thermoelectric figure of merit was enhanced remarkably over a wide temperature range of 323-523 K due to the high power factor and the maintenance of low thermal conductivity.