R y Fe 4 Sb 12-based filled skutterudites have been studied extensively as p-type legs used in high-temperature thermoelectric generator. One approach to further improve their thermoelectric performance is to optimize the overhigh hole concentration in R y Fe 4 Sb 12 skutterudite. In this study, we used element Mn doped on the skutterudite framework and systemically investigated the effects of Mn on the filler filling fractions, crystal structures, and high-temperature thermoelectric properties in Ce y Fe 4-x Mn x Sb 12. It is found that the Mn doping limit at Fe sites is around 0.15. Mn doping slightly enhances Ce filling fractions because Mn acts as an electron acceptor and its doping could push more electron donator Ce into the voids of skutterudites. Although Mn has one valence electron less than Fe , the excessive electrons donated by Ce fillers can completely compensate the holes generated by Mn and reduce the material's hole concentration, leading to a much reduced electrical conductivity and electrical thermal conductivity. Since the lattice thermal conductivities of Mn -doped samples are almost unchanged as compared with that of the matrix, the total thermal conductivities are obviously decreased. Meanwhile, high power factors are maintained in Mn -doped samples because of the enhanced Seebeck coefficient as well as the undegraded carrier mobility. As a combined effect, the figure of merit in Mn -doped samples is much improved in the whole temperature range. Sample CeFe 3.85 Mn 0.15 Sb 12 exhibits a maximum value of 0.98 at 800 K among all the samples investigated in this work.