The effects of the dopant (Mn) ratio on the microstructure and thermoelectric properties of FeSi_2 alloy were studied in this research. The alloy was fabricated by a combination process of ball milling and high pressure pressing. Structural behavior of the sintered bulks were systematically investigated by XRD, SEM, and optical microscopy. With increasing dopan (Mn) ratio, the density and varepsilon-FeSi phase of the sintered bulks increased and maximum density of 94% was obtained in the 0.07% Mn-doped alloy. The sintered bulks showed fine microstructure of alpha-Fe_2Si_5, varepsilon-FeSi and beta-FeSi_2 phase. The semiconducting phase of beta-FeSi_2 was transformed from alpha-Fe_2Si_5+varepsilon-FeSi phase by annealing.