Manganite-based heterojunctions La1−xCaxMnO3/SrTiO3:Nb (0.05 wt %) with x=0.1, 0.2, 0.33, 0.65, 0.75, and 1 have been fabricated, and the effects of Ca content on the interfacial potential are experimentally studied. Rectifying behavior well described by the Shockley equation is observed, and the interfacial potential (VD) is obtained for all of the junctions based on an analysis of the current-voltage characteristics. The most remarkable result of the present work is the strong dependence of the interfacial potential on the carrier content of La1−xCaxMnO3 films: VD increases monotonously from ∼0.6 to ∼1.1 V as x sweeps from 0.1 to 1. Influence on VD of the Fermi energy and Jahn–Teller effect in La1−xCaxMnO3 films are discussed. © 2008 American Institute of Physics.