We study theoretically the interracial electronic property of a heterojunction made from two Mott insulators (MI)with different magnetic structures.By means of unrestricted Hartrce-Fock calculations in real space,we find that a charge dipole can form spontaneously near the interface of the MI/MI heterojunction.The magnitude of this charge dipole depends strongly on the magnetic states of both sides of the heterojunction.Combining with the result from an exactly solvable two-site toy model,we argue that the interface dipole arises from exchange effects as well as its asymmetry intrinsic to the heterojunction near the interface.Our study may shed light on the fabrication of ultrathin ferroelectric and magnetoelectric devices.