0.935BaTiO3-0.065(Bi0.5Na0.5)TiO3+xmol%MnO2 (BBNTM-x) ceramics with 0≤x≤0.05 were fabricated with muffled sintering by a modified synthesis process. Their microstructure and enhanced positive temperature coefficient of resistivity (PTCR) characteristics were systematically investigated in order to obtain lead-free high TC PTCR thermistors. All specimens showed a perovskite structure with a tetragonal symmetry and no secondary phase was observed. Grain growth was achieved when the doped MnO2 was increased above 0.02 mol%. This is due to the effect of positive Mn ion doping as an acceptor compensating a Ba vacancy occurred by the higher donor dopant concentration of Bi3+ ion. Especially, enhanced PTCR characteristics of the extremely low ρRT of 99 Ω·㎝, PTCR jump of 5.1×10(3), α of 15.5%/℃ and high TC of 167℃ were achieved for the BBNTM-0.04 ceramics.