Vapor doping affects the PTCR effect in BaTiO3 ceramics distinctly. Doping B2O3 vapor in BaTiO3 results in the expanding of the grain lattice cell. Thus, boron interstitial may get into BaTiO3 grain lattice. The room temperature resistance of Y-BaTiO3 decreases and the PTCR effect increases distinctly through the doping of B2O3 vapor. Given the same sintering condition, doping with higher level of the vapor B2O3 source results in the higher PTCR effect. The interstitial boron ion and/or its complex can act as trap center and enhance the PTCR effect of the ceramics.