A manganite p-n heterojunction composed of La0.67Ca0.33MnO3 film and 0.05 wt% Nb-doped SrTiO3 substrate is fabricated. Rectifying behavior of the junction well described by the Shockley equation is observed, and the transport properties of the interface are experimentally studied. A satisfactorily logarithmic linear dependence of resistance on temperature is observed in the temperature range 100-360 K, and the linear relation between activation energies deduced from the R-1/T curves and bias is observed. According to the activation energy, the interfacial barrier of the heterojunction is obtained, which is 0.92 eV. The present work implies that such heterojunction can be used as a temperature control and measure device.